摘要:

The present study has set forth a hypothesis of impermeability characteristics of caking coals. The impermeability of coal in plastic state to gas is an extremely important property of caking coals. The formation of impermeable plastic mass is a necessary condition for the caking and coking process. The impermeability creates a cage effect for physiochemical surface process which is caused by and promotes complicated chemical interractions between pyrolysis products. The determination of impermeability in plastic state of coal along with other related parameters should be beneficial for making an overall evaluation of caking behavior. Based on the penetrative plastometer, a modified experimental instrument was designed and constructed. The unique advantage of measuring impermeability of coal in its plastic state by this instrument is providing a means to synthesize the impermeability with other data such as volumetric shrinkage and coke quality. The parameters for identifying impermeability of various coals have been recognized as the maximum value of resistance, the initial temperature of intense rising resistance and the temperature of maximum resistance. The impermeability of coals in plastic state depends on their original properties. Nevertheless, experimental results had shown that the impermeability could be improved by way of regulating processing conditions. This in turn may be helpful to broaden the marketability of otherwise inferior caking coals.

ISSN:0094-243X    

DOI:10.1063/1.32917

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A model study of the rheological behavior of the coal melt is proposed. Effects of intragranular heat and mass transfer, particle size, porosity, deformation of viscous melt, etc., are considered, so as to explain the striking phenomena of swelling and shrinking deformations for a single particle at various heating rates. This model gives both qualitative and quantative descriptions of the transient swelling characteristics, particularly the ’’cenosphere’’ formation during the pyrolysis of bituminous coal. The theoretical predictions show reasonable agreement with the experimental observations of microscopic studies.

ISSN:0094-243X    

DOI:10.1063/1.32918

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The United States MHD Program has set as its goal, the development of a fullscale, coal‐fired, MHD power plant some time in the mid to late 1980’s. Because of the severity of the MHD environment, systematic materials characterization is necessary when studying high‐temperature materials, especially for use with coal. Experiments are underway to characteristize Montana coal slags and the ceramic materials they come into contact with. The inorganic constituents of coal remaining after high temperature combustion in an MHD (Magnetohydrodynamic) power plant conbustor form an iron‐rich, ’’dirty’’ glass whose electrical properties are important to the operation of the MHD generator. In particular, alkali ’’seed’’ (K2CO3) is added to enhance the conductivity of the plasma so the slag layer which coats the walls and electrodes of the generator is rich in K2O. We present results of a systematic study of the electrical conductivity of a Rosebud coal ash with graded amounts of K2CO3added. At high temperatures, the conductivity curves are smooth with several ionic species contributing. At lower temperatures the curves become more complex with the presence of crystalline phases in the glass.

ISSN:0094-243X    

DOI:10.1063/1.32919

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Iron sulfides in the form of ferrimagnetic pyrrhotite have been removed from solvent refined coal by the use of high gradient magnetic separation. The results of such separations have been correlated with those of studies of the thermochemical and magnetochemical properties of the undissolved solids present in the product of coal liquefaction. Complete inorganic desulfurization was achieved at the same temperatures at which the solids exhibit a maximum magnetization, at about 230 °C. The preferred form for the highest magnetization is a monoclinic structure with a composition of Fe0.875S. Where the sulfides do not occur in this form, it has been possible to convert them to the high magnetization state by exposure to a hydrogen sulfide atmosphere at an elevated temperature. To approximate the temperature cycle experienced by the liquid coal coming from the reactor toward the filter, samples were heated above the Curie point to destroy the magnetization and then cooled to about 260 °C for H2S treatment. Measurements on the solids subsequently extracted showed a striking increase in the magnetization compared to the untreated material.

ISSN:0094-243X    

DOI:10.1063/1.32922

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

It has recently become popular to describe coal structure as a macromolecular polymer network. In order to quantitatively test this model and to study the influence of the physical structure of coal on liquifaction and gasification reactions, it is desirable to develop spectroscopic techniques which can be used to probe network and molecular properties. This has been difficult due to the high absorption of coal and heterogeneity of samples. We have used microspectrophometric techniques to measure absorption spectra in the near‐UV and visible using a scanning microspectro‐photometer and in the IR using a Fourier Transform IR spectrometer. Samples were prepared with thicknesses ranging from 500A˚ to 2 &mgr;m and areas to 0.5 mm2. Broad featureless absorption are observed in the near‐UV and visible and cannot be solely explained by either light scattering from the inhomogeneous coal network or the absorption of a heterogeneous misture of organic components. The IR spectra show well resolved features and computer techniques can be used to eliminte background due to light scattering artifacts.

ISSN:0094-243X    

DOI:10.1063/1.32923

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The high‐temperature ash levels of some typical U. S. bituminous coals can be rapidly estimated with a standard error (absolute) of 1.7% ash from simple linear correlations between % Si and % ash. Si contents may be rapidly determine by Fast Neutron Activation Analysis (FNAA), X‐Ray Flourescence (XRF), or Slurry‐Injection Atomic Absorption Spectrometry (SIAAS) methods requiring little more sample preparation other than a brief grinding and weighing. These three instrumental methods showed roughly equivalent correlations. In contrast to earlier reports, logarithmic plots do not produce improved estimates. Also, correlations do not seem to be significantly improved by selecting coals within one rank or from one geographical area. The slurry‐injection atomic absorption method does not require significant modifications of existing commercial AA instruments. The conventional method for determining ash content of coal, though simple and accurate, requires a considerable amount of time in the laboratory. Ash content of coals is an important parameter related to their eventual use as fuels, as feedstocks in liquefaction and gasification processes, and in metallurgical processes.

ISSN:0094-243X    

DOI:10.1063/1.32925

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Recently, Coughlin et al. have shown that a redox couple involving the oxidation of coal and the reduction of H+at the cathode and primarily CO2at the anode. We have examined the electrochemical behavior of various Kentucky coals and H‐Coal liquids at platinum electrodes under voltammetric and electrolytic conditions, and found that the reported electrochemical process is not a general one, and that Fe++may yield a similar phenomenon. Thus, agueous 0.1M LiClO4slurries of most coals were found to yield characteristic voltammograms containing anodic waves starting at +0.4 volts vs. SCE and extending throughout the positive potential range. The resulting oxidation currents were proportional in magnitude to the coal concentration employed. Upon filtration, the bulk of the electro‐activity of the coal slurry was found to be retained in the filtrate while the remaining coal residue showed drastically diminished currents upon formation of a new slurry. Atomic absorption analysis of the filtrate revealed iron concentrations in the parts‐per‐thousand range. It was determined that the half‐wave potential of Fe2+occurred at +0.45 volts under the conditions employed. Also, acetonitrile coal slurries and acetonitrile solutions of H‐Coal liquids exhibited no larger electrolysis currents than were obtained with blank solutions.

ISSN:0094-243X    

DOI:10.1063/1.32927

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

57Fe Mo¨ssbauer spectra have been taken of bed‐moist and dried samples of Latrobe Valley brown coals. The samples contain iron concentrations of 0.07‐1.8% and cover the known variations in the field. The bed‐noise samples (67% water) typically gave several poorly resolved doublets in the region −0.3 to +0.6 mm s−1w.r.t. Fe metal, with maximum absorption dips of 0.1‐0.3%. In contrast to work on higher rank, higher sulphur U. S. coals, only one of our coals had detectable amounts of pyrite. The remaining absorption lines could not be assigned to any known minerals or clays. The isomer shift and quadrupole splittings could corrspond to either low‐spin FeIIor to trivalent Fe and we believe that they are all due to hydrated organically bonded iron. Measurements at 78 K on one sample which was allowed to dry in air (&angupr;20% water) showed an increase of a factor of 10 in the absorption (Debye‐Waller factor) and a completely changed spectrum. We take this as evidence that the iron atoms have principally water ligands in the bed‐moist state. Dried and briquetted samples gave a large intensity (3%) doublet due to organically bonded Fe and one or more washed‐out hyperfine fields of 55 T, 48 T and 33 T probably corresponding to haematitie, goethite and organically bonded iron respectively. One sample also contained szomolnokite as an oxidation product from pyrite.

ISSN:0094-243X    

DOI:10.1063/1.32928

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Air/water Oxydesulfurization has been demonstrated in autoclave experiments at the Pittsburgh Energy Technology Center for various coals representative of the major U. S. coal basins. The applicability at present of this treatment for producing an environmentally acceptable coal has been restricted by recently proposed SO2emission standards for utility boilers. The product would, however, be attractive to the many smaller industrial coal users who cannot afford to operate and maintain flue gas desulfurization systems. It is also possible that the utility industry could realize a benefit by using chemically cleaned coal with partial flue gas scrubbing. The higher cost of the cleaned coal would be offset by the reduction in capital and operating costs resulting from decreased FGD requirements. The susceptibility of sulfur in coal to oxidative removal varies with the nature of the sulfur‐containing species. The inorganic sulfur compounds, primarily pyrite, marcasite, and iron sulfate, are more amenable to treatment than the organically bound sulfur which exhibits varying degrees of resistance depending on its chemical environment. Air/water Oxydesulfurization consistently removes in excess of 90 percent of the pyritic sulfur; the extent and efficiency of organic sulfur removal however, depends on the type of coal and severity of treatment used. In general, the organic sulfur of the higher rank coals exhibits more resistance to treatment than that of the lower rank coals; however, the accompanying heating value is greater for the latter. Similar treatment of sulfur‐containing model compounds further illustrates the relative susceptibilities of different chemical species to oxidation. Application of these data to the understanding of the complex chemistry involved in the treatment of coal is a preliminary step toward improving the efficiency of Oxydesulfurization.

ISSN:0094-243X    

DOI:10.1063/1.32930

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Preliminary observations suggest the utility of liquid sulfur dioxide for desulfurization of coal. Initial exploratory work has demonstrated that under mild condutions: (1) between 35 and 70% of theorganicsulfur can be removed from selected coals, (2) extraction of a variety of organic materials from the coal occurs, (3) comminution of selected coals is extensive, and (4) pyrite can be oxidized. Results obtained as functions of temperature and added reagents will be presented. Hypotheses concerning the origins of these observations will be considered and present limitations of the methods will be outlined. The support of this research by the U. S. Department of Energy and the samples supplied by the Coal Research Section, College of Earth and Mineral Sciences, Pennsylvania State University are gratefully acknowledged.

ISSN:0094-243X    

DOI:10.1063/1.32931

出版商:AIP    

年代:1981

数据来源: AIP