Series Of Coals Research Articles

Influence of structural parameters on coal char gasification: 1. Non-catalytic steam gasification

Various coal chars prepared at 750 °C from a series of coals ( wt% C = 66.1–88.1daf) and at 240–1000 °C from one coal (% C = 81.9), were gasified at 800–850 °C with an equimolar H 2OHe or equimolar H 2OH 2 mixture. The structure of the char was characterized by X-ray diffraction and gas adsorption measurements and compared with the reactivity. It was found that a crystalline structure parameter obtained by the X-ray method sensitively reflected the reactivity of the char.

Reactivity of coal macerals and lithotypes

Variations in the rank of coal used for power generation can cause problems with the efficiency of combustion. This paper describes an examination of the effects of variations in the maceral composition of coals, in association with rank, upon reactivity in combustion. Using a simple reactivity test, the reactivity ranges for two rank series of single seam coals were determined along with the reactivity ranges obtained from studying lithotypes of various maceral concentrations of a single coal. Reactivity tests on pure maceral concentrates show significant reactivity differences between macerals so that coal type (maceral/lithotype content) must be considered as important a parameter as rank. Changes in maceral concentration alone could account for 45% of the rank reactivity variation without changing rank.

Characterization of some coals and coal intercalations by high-resolution 1H (BR-24/MAS at 270 MHz) and 13C (CP/MAS) n.m.r. in solids

High resolution 1H n.m.r. studies combining the BR-24 multiple-pulse method after BURUM and RHIM with fast magic-angle sample spinning (MAS), and high resolution solid-state 13C n.m.r. measurements with cross polarization (CP) and MAS have been used for investigating: a number of coals of different ranks; GDR soft brown coals characterized by textural differences; and typical intercalations to be found in such soft brown coals. The resolution level of 1H n.m.r. spectra achieved so far at a resonance frequency of 270 MHz permits determination of essential functional groups. The coalification series ranging from soft brown coal to anthracite shows an increase of the aromaticity values ƒ a C and also an increase of the ƒ a H values, which is analogous to the increases in reflectance and carbon content. There are marked differences between the functional groups to be found in detrital and xylite-containing soft brown coals. Tertiary (Miocene) brown coals from the 2nd Lower Lusatian seam (GDR) (i.e. unbedded, poorly bedded, bedded, xylite-containing unbedded, and gelified bedded coals) differ significantly due to variations in micropetrographical composition. Varying amounts of cellulose and lignin are contained in the xylites of the 2nd Lower Lusatian seam. 13C and 1H n.m.r. measurements are employed to determine the main constituents of substances such as pyropissite, retinite, fusite and ‘monkey hairs’ (fossilized rubber).

Geochemical Effects of Primary Migration of Petroleum and Their Relevance with Respect to Mechanisms and Efficiencies of Expulsion: ABSTRACT

Geochemical analysis of the petroleum residing in the pore system of source rocks after primary migration has occurred holds the key to better understanding the mechanisms and efficiencies of expulsion processes. Indeed, the detailed recognition of migration phenomena and quantification of their effects have been made by a combined approach which (1) examines the composition variation of residual oil within individual bodies of source rocks and its relationship to, inter alia, petroleum in juxtaposed reservoir rocks and (2) makes a material balance of petroleum-related chemical species. This approach has been applied in three separate case studies, two of which address the economically most important source rock units of central and northwest Europe: the Lower Jurassic Toarcian shales from the Hils syncline area (Federal Republic of Germany) and the Upper Jurassic Kimmeridge Clay Formation from the Brae field area, North Sea (U.K. Sector). The third study is of a series of coals and interbedded sediments of Late Carboniferous age from the Ruhr area (Federal Republic of Germany). A synthesis of results has revealed some fundamental differences in migration mechanisms and efficiencies which are strongly linked to organic richness, kerogen quality, and source rock fabrics. These differences concern especially the degree ofmore » microfracturing and the role of gas as transport agents.« less

Chemical characterization of Hungarian brown coals by curie-point pyrolysis-low-energy electron impact mass spectrometry and multivariate analysis and by curie-point pyrolysis-gas chromatography-photoionization mass spectrometry

A series of Hungarian Miocene brown coals were analysed by pyrolysis-low-energy electron impact mass spectrometry and discriminant analysis. Correlation patterns in the mass peaks of these brown coals coincided with the geothermal history determined from the reflectivity of the macerals. Coal rank and the first discriminant function had a correlation coefficient of 0.96. Discriminant analysis also classified the coals according to their depositional environment. The mass peaks were deconvoluted using pyrolysis-gas chromatography-mass spectrometry data obtained under low-energy photoionization conditions. Several apparently homologous series of mass peaks in the pyrolysis-low-energy electron impact mass spectra were found to represent entirely different types of pyrolysis products. The low-energy fragmentation patterns of isoprenoid and alicyclic hydrocarbons are substantially different from the usual 70 eV electron impact spectra and may cause erroneous interpretation of non-deconvoluted pyrolysis-low-energy electron impact mass spectrometric data. The deconvoluted pyrolysis-low-energy electron impact mass spectrometric data resulted in a more detailed reconstruction of the original environments of deposition. Marine influences were deduced from several types of organic sulphur compounds. Markers for lignified wood, leaf and root remains and resins were present in the pyrolysates.

Occurrence and transformation of phyllocladanes in brown coals from Nograd Basin, Hungary

Phyllodactanes are the major components of the lipid extracts of two series of brown coals from the Nograd Basin (Northern Hungary). In this basin coalification was induced by thermal stress of volcanic origin which determined the isomeric composition of these compounds. Depending on the degree of maturation the 16α(H)-isomer decreases in abundance relative to the more geochemically stable 16β(H)-isomer, the presumed equilibrium ratio being 0.3. Laboratory thermal degradation experiments have confirmed the feasibility of this transformation, showing that phyllocladene and isophyllocladene are intermediate products of the process. Variable amounts of retene and simonellite are also found, but no evidence is obtained of abietane-type precursors. Nevertheless, a close relationship of the retene-phyllocladane ratio with maturity, represented by the H C ratio, is observed. As an explanation, it is suggested the thermally induced formation of retene from phyllocladanes, simonellite being an intermediate of the proposed reaction. Further evidence for this hypothesis has been obtained from laboratory simulation experiments. Finally, the presumed isomerization and aromatization rates of these diterpenoids have been compared for the series of samples, pointing to a promising tool for assessing the geochemical history of coal basins.

Processes controlling the composition of acid sulfate solutions evolved from coal

Leaching of a series of Appalachian coals by distilled water has been studied in laboratory reactors. From columns open to air at 25°C, leachates were produced containing typically about 0.2 M SO 4 2−, 0.1 M total Fe and having pH < 2. Leachates contained high concentrations of toxic trace metals, including Be, Al, Cu and Cd. Concentrations of sulfate and Fe in leachates from different coals were similar and were not related to concentrations of total S in the coals. Saturation with respect to melanterite (FeSO 4·7H 2O) and a ferric oxyhydroxide phase was observed in most solutions. Leachates were undersaturated with respect to anhydrous ferric sulfate and Na-jarosite, but supersaturated with respect to K-jarosite, suggesting that none of these phases controlled solution composition. The ratio of total ferric Fe to total ferrous Fe normally exceeded unity. Accumulation of ferric Fe indicates either that its reaction with pyrite is inhibited in weathered coals, or that the coals contain pockets of oxidized pore fluid that are out of contact with pyrite. Release of Be correlated with release of Al, and release of Cu correlated with release of Fe. Reducing the temperature, lowering the partial pressure of oxygen or adding limestone retarded the release of pyrite oxidation products from the coals. Addition of limestone should be considered if it is necessary to control release of acid leachates from coal piles.

Comparison between extracts from natural and artificial maturation series of Mahakam delta coals

Immature type III organic matter from the Mahakam delta (Indonesia) was heated for 24 hr from 250 to 400°C in a closed and very confined medium, under pressures of 500 and 1000 bars with and without water. Comparative experiments were performed in an open-pyrolysis system. Likewise, natural samples from the same provenance and of increasing maturity were selected as a natural reference series. Hydrocarbons released naturally and artificially were studied by liquid chromatography fractionation and capillary gas chromatography. When artificial maturation is performed with confined pyrolysis, most of the quantitative and qualitative aspects examined show a fair simulation of natural evolution, even though some discrepancies might possibly be detected when molecular aspects are examined. On the other hand, the use of open-system pyrolysis does not at all duplicate the natural behavior. Comparison with the existing literature shows that the method described here seems to lead to the most complete results. We concluded that the role of confinement seems to be essential, the role of water seems to be surbordinate, and the role of increasing external pressure to be nil, at least in the pressure range investigated.

Chemical characteristics of liptinite macerals in humic and sapropelic coals

According to previous studies alginite does not occur in humic coals. However, in coals from the Saar District, F.R. Germany, alginite was identified by fluorescencemicroscopy. In addition, high amounts of an undeterminable liptinite maceral were found and tentatively explained as an alteration product of alginite. Therefore, organic geochemical methods were used to characterize and identify this unknown liptinite maceral. Organic geochemical parameters such as CPI, pristane/phytane ratio and methylphenanthrene index, show not only a dependence from coal rank but also yield additional information about the type of organic matter input and the depositional environment of the coals. A series of coals of different origins around 0.8% vitrinite reflectance were investigated, to determine how far the geochemical parameters reflect change in facies. The samples included cannel, boghead and resinite-rich coals, as well as isolated durain bands. With increasing amounts of alginite in the coal, the CPI, pristane/phytane- and C 4-naphthalene/phenanthrene ratios of the extracts decrease. As illustrated by two representatives samples, some resinite- and sporinite-rich coals show a primarily naphthalene derived aromatic composition, whereas some alginite-rich coals of the same rank show phenanthrene and its derivatives to be dominant. With respect to technological properties most coals from the Saar District correspond with a higher rank than indicated by reflectance measurements. Those coals in general show lower values of the aforementioned ratios in comparison with Ruhr coals of similar vitrinite reflectance values.

Structural investigations of Australian coals—VI. The effect of rank as elucidated by per trifluoroacetic acid oxidation

Several techniques including gas chromatography, petrography, nuclear magnetic resonance and infrared spectroscopy are applied to the investigation of pertrifluoroacetic acid oxidation of a series of Permian Australian bituminous coals in order to probe the effects of maturation on aliphatic structure. The occurrence of insoluble oxidation products is attributed to reagent blocking by carboxylated aromatic species. The combined influence of maturation and semifusinite content is reflected in the concentration and structural composition of functionalised long chain aliphatic oxidation products.

Coal combustion: Correlation between surface area and thermogravimetric analysis data

A series of coals of different rank has been characterized by surface area measurements performed by sorption of both nitrogen and carbon dioxide. While the data obtained with nitrogen do not discriminate among the different coal samples, those based on carbon dioxide sorption do give a significant distinction between the samples. This technique has also been applied to the determination of the surface area of coal samples quenched after stepwise combustion in air atmosphere. It has been possible to establish a useful correlation between the latter data and the burning profile measured by derivative thermogravimetry. The aim of the present study was to gain a better understanding of the coal combustion process on a laboratory scale which could reasonably be extended to combustion plants. The results presented are relevant to some of the multivalent aspects inherent in the coal combustion process and some valuable information has been gained in respect of characterization of solid fuels.

Examination of some effects of dry cooling on coke quality

A series of coals were carbonized, on the 250 kg scale under standardized conditions, to provide both dry-cooled and wet-quenched cokes which were subsequently subjected to reactivity and strength testing. The data from the tests of reactivity to CO 2 at ≈1000 °C support the view that dry coke cooling leads to lower reactivity, but examination of the porous structure in the pore size range > 5.45 μm and of the optical anisotropy of the coke carbon revealed no changes to account for this effect. Although the micum test indices were sometimes improved by dry coke cooling, the differences were not statistically significant. On the other hand, there was clear evidence of increased coke tensile strength. The effect of dry coke cooling on coke properties appears to be sufficient to exert some influence on the blast furnace coke rate and thereby on the economy of the dry-cooling process.

Comparison between natural and artificial maturation series of humic coals from the Mahakam delta, Indonesia

Type III (humic) organic matter from the Mahakam delta (Indonesia) was chosen to compare artificial and natural coal series. Powdered and concentrated immature organic matter was heated in sealed gold tubes for 24 hr at temperatures ranging from 250 to 550°C and under pressures ranging from 0.5 to 4 kb, with and without water. Both elemental and Rock-Eval analyses were used to characterize the products. A comparison between our results, published data and the natural model shows that, quantitatively, natural maturation is simulated better when pyrolysis is performed under confined conditions (no free volume, no diluting inert gas). Thus, pyrolysis in a medium swept by an inert gas, vacuum pyrolysis and some pyrolysis in sealed glass tubes must be considered to be poor simulation tools. The presence of water does not seem to have an essential effect. Allowing the hydrocarbons formed to reach a certain value of partial pressure seems to be important. Results are unchanged when external pressure varies from 0.5 to 4 kb.

Determination of total fluorine in coal by the combustion-hydrolysis/fluoride-ion selective electrode method

A rapid analytical method has been developed for the determination of fluorine in coal. Coal is mixed with quartz sand, then burnt and hydrolysed in steam and oxygen at 1100 °C, whereupon the different forms of fluoride in coal become solubilized. The fluorine is determined with a fluoride-ion selective electrode. The method proposed is not affected by the ash content of the coal. The obtained solution has a simple ion composition and a low blank value giving the method potential as a fluorine determination technique. A series of typical coals have been tested and the agreement between the proposed method and the ASTM method and alkali-fusion method is satisfactory. Two sedimentary rock standards have been analysed and the results are within permissible limits of error. The method is considered to be accurate and reliable, and is first compared with the half-fusion method.

Chloroform extracts of a series of coals from the Mahakam delta

A detailed study of the changes that take place in the organic solvent extractable organic matter during the early stages of thermal maturation has not been published to date. The present work describes several trends occuring with increasing diagenesis, observed in the chloroform extractable organic matter of a series of coals of Tertiary age from the Mahakam delta (Indonesia), with special consideration given to the lignite and sub-bituminous stages. Wide variations in the values of the total chloroform extracts were observed in this work and the extraction yields reached a maximum at the beginning of the sub-bituminous stage. This maximum is discussed and two hypotheses are offered which may provide an explanation for the trend. These are the formation of extractable compounds by defunctionalisation of kerogen during the lignite stage, followed by a defunctionalisation of compounds in the chloroform extract itself during the sub-bituminous stage, and/or a migration from deeper horizons.

Effect of surface functional groups on the flotation of coal

The flotation behavior of a series of coals is described in terms of the predominant oxygen-containing functional groups. These groups control not only the thermodynamics, but also the kinetics of coal flotation. It is shown that the maximum flotation response occurs close to the isoelectric point of the demineralized coal. The correlation between content of phenolic and carboxylic groups and the flotation response of a range of coals was found to be excellent. Functional groups control coal wettability through the balance of hydrophobic/hydrophilic sites, and control flotation kinetics by their influence on surface charge.

Naturally Occurring High-Chloride Coal and Superheater Corrosion—A Laboratory Study

DOE Provided funds for C-E to investigate the fireside corrosion potential of commercial boiler tube alloys at elevated temperatures when exposed to the combustion products from a series of coals. The results of the laboratory and field tests were previously reported. In a supplementary phase of the program, C-E tested for the effect of chloride on similar alloys while firing a naturally occurring high chloride Midwestern bituminous coal in the same laboratory furnace. On the basis of exposure in the convection pass at temperatures from 1100–1700°F, Inconel Alloy 690 was found to have very good resistance to corrosion while Incoloy 800H and Tp-310 s. s. were good transitional materials. Poor materials were T-22, 316 s. s., Inconel 617, and Inconel 671.

Determination of trace elements in coal by an oxygen bomb combustion/atomic absorption spectrophotometric method

A rapid analytical method has been developed for the determination of such trace elements as beryllium, chromium, copper, lead, manganese, nickel, vanadium and zinc in coal. Coal is combusted in the standard Parr oxygen bomb. When contamination from the bomb wall occurs, the bomb is equipped with a quartz liner. The trace metals in the residue from combustion are determined by flame atomic absorption spectrophotometry. The method has been evaluated on a series of coals, including three National Bureau of Standards Standard Reference Materials (NBS-SRMs). Comparison of this method and the American Society for Testing and Materials (ASTM) Standard Test Method D 3683 demonstrated that accurate and precise results can be obtained when coal samples are prepared in the Parr oxygen bomb. Sample preparation time is greatly reduced over normal ashing procedures.

Reactivity of coal towards hydrogenation—ranking by kinetic measurements

Rate data on liquefaction of a series of low pyrite bituminous coals in tetralin at 400 °C have been measured. Rates of disappearance of coal and rates of formation of oils, asphaltenes, and preasphaltenes have been determined, and kinetic parameters for coal disappearance calculated based on a second-order rate expression. The usefulness of kinetic rate constants as sensitive reactivity ranking factors is demonstrated.

Example of the enrichment of carbon-13 in coals in the process of coalification

δ13 C measurements on a series of coals from the Mahakam delta (Kalimantan, Indonesia) show a progressive increase from ≈ − 29.5% at the peat-lignite transition to ≈ − 27.5% at a reflectance of R 0 ≈ 0.9. Given the very good homogeneity of the series, the shift is likely to be due to coalification. However, a coalification model based on this trend and the release of C0 2, H 20 and CH 4 indicates δ13 C values of C0 2 which are very low as compared to currently accepted figures.