Coal Lithotypes Research Articles

97/01698 Alternative feedstock for manufacture of pitch needle coke from coal-derived material

Because of the short supply of high-quality coking coals in certain areas of the world, many methods of improving the coking characteristics of poorly coking or noncoking coals have been examined as alternatives to importing more expensive, better quality coals. Co-carbonization, or the addition of coal-derived or petroleum-derived materials to the coal charge prior to carbonization, has been used on a commercial basis in the Japanese coking industry. These additives have been used in both solid and liquid form as binders in coal briquettes or as direct additions to the coal blend.In this study three different coal lithotypes were sampled from each of three United States bituminous coal seams: (1) a marginally coking high-volatile B-rank Illinois No. 6 Seam; (2) a highly fluid, good coking quality, high-volatile A-rank Pittsburgh Seam; and (3) a strongly coking low-volatile Blue Creek Seam. Each lithotype sample was carbonized in small-scale (50 g) charges with each of three additives at 0, 2, 5, and 10% additive by weight. The additives included ASP, an asphalt pitch; KRP, a petroleum residue pitch; and SRC, a solvent-refined coal product. The different lithotypes were sampled to examine the effects of coal type as well as rank. A micro-tumbler test was used to give at least a relative coke-strength value for the cokes produced. In addition, all the cokes produced were examined microscopically to determine the effects of co-carbonization on the coke structure.The Illinois No. 6, Pittsburgh, and Blue Creek Seam coals all showed substantial strength increases when co-carbonized with 2, 5, and 10% of each of the three additives, particularly at the 5 and 10% levels. The SRC appears to be the best additive overall for the three ranks of coal, as judged by its ability to combine with the coal to make a higher strength coke. There appear to be no conclusive coke-strength differences among lithotype samples for any of the three coals, probably because of the small scale of the tests and the relatively small differences in inert maceral content among the lithotypes. Five percent by weight of additive appears to be sufficient, if properly blended with the coal charge, to produce higher strength cokes. This is also probably the maximum economically viable level, particularly in the United States coking industry. Two percent is probably the minimum additive level for adequate mixing on a commercial scale.

Variation in permeability with lithotype and maceral composition of Cretaceous coals of the Canadian Cordillera

The permeability of high- and medium-volatile bituminous Cretaceous coal at the megascopic and microscopic scale is investigated utilizing a pressure-decay permeameter. The order of decreasing permeability with lithotype is: bright (average = 4.1 md), banded (0.79 md), fibrous (0.50 md), banded dull (0.14 md) and dull (0.016 md). Bright coals are the most permeable because of associated macro-fracturing (cleat). Banded dull coal permeability generally increases with increasing vitrinite content. The lowest permeabilities occur in dull coals with a high mineral and inertinite content. Fibrous coal has a higher permeability than dull coal of the same rank due to the abundance of macroporous fusinite in fibrous coal. Dull coal permeability decreases with an increase in rank, but these results are overshadowed by compositional variability between samples. Pressure-decay measurements are more reliable for dull lithotypes as these lithotypes do not fracture as easily during sample preparation. Although measured permeabilities are optimistic due to the relaxation of stress upon exposure of coal to atmospheric pressure, the results obtained are representative of the range of permeabilities of coal lithotypes and provide insight into the variability in permeability that may exist at high effective stress in the subsurface.

Maceral/microlithotype analysis of the Hardgrove grindability of lithotypes from the Phalen coal bed, Cape Breton, Nova Scotia

Three lithotypes of Phalen coal from Cape Breton County, Nova Scotia, Canada, were subjected to a modified Hardgrove grindability index (HGI) test. The testing scheme differed from conventional (ASTM D-409) Hardgrove testing by, in one case, repeating the test three times prior to removing the -200-mesh fine coal from the Hardgrove mill, and, in a second test, removing fines after each of three successive Hardgrove tests. Only the first stage of the latter testing scheme actually conforms to the standard HGI test. All processed samples were analyzed petrographically by a combined maceral/microlithotype analysis. The increase in the percentage of coal ground to -200 mesh increases through the 60- to 180-mesh fractions for each of the lithotypes for the following two apparent reasons: First, with progressive grinding, more of the oversize material is close to 200 mesh (75 μm), creating a “pool” of particles ready to be ground to -200 mesh, and, second, the removal of fines from the system at each step eases the grinding at the successive step. The fines retained system shows the influence of buffering of further grinding by the particles retained in the grinding mill. The Phalen lithotypes and the series of Central Appalachian coals, evaluated previously by Hower and Wild (1994), differ in that an increase in vitrite and a decrease in trimacerite is observed in successive -200-mesh fractions in two of the Phalen lithotypes. This is the opposite of the trend observed in the slightly lower-rank Central Appalachian coals.

Mössbauer spectroscopic investigation of low rank coal lithotypes

Abstract Low rank coal lithotypes — xylain, humovitrain, semifusain, fusain and liptain sampled from the Maritsa Iztok coal basin (Bulgaria) have been examined by Mössbauer spectroscopy with no pre-concentration procedures. The results are used to identify three iron species in coal lithotypes and show that covalent iron (Fe II ) related to pyrite, is the main iron species in xylain, while in humovitrain ferric iron is dominant. The total quantity of iron species in semifusain, fusain and liptain is about the same, but their distribution is different. Ferric iron dominates in all the three lithotypes. Ferrous iron, although present in smaller quantities, has a higher content in fusain than in semifusain. Our results illustrate the type of oxidation processes which formed the coal lithotypes. A transformation of Fe 2+ to Fe 3+ has occurred out as a result of differing oxidation processes. The intensity of that transformation increases during the destructive microbial oxidation and decreases during thermal oxidation and direct oxidation processes. The opposite transformation of ferric to ferrous iron has been achieved during both thermaloxidation and direct oxidation processes.

Analysis of coal banding texture and implications for megascopic image analysis

Window filtering methods were modified to analyse megascopic textural information acquired from banded bituminous coal seams in the field. Although banding texture directly influences the physical properties of coal, methods for its characterisation and analysis are poorly developed. Banding texture was obtained manually from the coal face and core at a minimum resolution of 1 mm. Window filtering was used to determine the optimum resolution (30–50 mm) required for accurate discrimination of coal lithotypes by either manual or image analysis methods. Methods used to automate this procedure and their problems are discussed.

96/05657 E.p.r. studies of thermal decomposition of exinite and inertinite

Electron paramagnetic resonance (EPR) spectroscopy was used to analyse properties of paramagnetic centres systems of the samples separated from two lithotypes of Polish coal (85.6 wt% C). The EPR spectra of the durain samples with a content of 2–22 vol.% exinite, 73–86 vol.% vitrinite and 5–17 vol.% inertinite, and the clarain samples with a content of 3–14 vol.% exinite, 65–90 vol.% vitrinite and 4–32 vol.% inertinite were compared. Three different groups of paramagnetic centres in each of the coal samples were found. The concentration of unpaired electrons and the parameters of the resonance absorption curves: linewidths and g-factor, were determined.

96/03492 Kinetic studies on low temperature oxidation of low rank coal lithotypes by molecular oxygen

96/03492 Kinetic studies on low temperature oxidation of low rank coal lithotypes by molecular oxygen

96/04509 Images of demineralized coal surfaces by scanning tunnelling microscopy

Five Tertiary deposits in the Czech Republic were studied using coal petrological and organic geochemical methods. Coal samples were chosen to cover four lithotypes: xylite rich coal, matrix coal, liptobiolith, and sapropelic coal. Xylite rich and matrix coals are characterized by higher ulminite and densinite contents, and lower textinite and resinite contents. Sapropelic coals from the North Bohemian and Žitava basins are formed by large amount of ulminite and densinite, and a high proportion of liptodetrinite, sporinite and alginite that prevails in sapropelic shale from the Uhelná relic. The essential difference between sapropelic coal and liptobiolith coal consists of high contents of liptodetrinite, bituminite, resinite, inertinite, and lower contents of clay minerals in liptobioliths. The biomarker composition of the aliphatic fraction includes n-alkanes, and their distribution varied according to coal lithotype: long n-alkanes were dominant in liptobioliths, sapropelic coals and shale, the mid-chain n-alkanes prevailed in xylite rich coals, and the short-chain n-alkanes were abundant in matrix coals. The prevalence of diterpenoids represented by phyllocladane type compounds indicated the presence of gymnosperm vegetation. Molecular indicators for angiosperms, present mainly as oleanenes, were also recognized in the lignite samples. Hopanoids were represented mainly by 17α(H),21β(H)-homohopane and hop-17(21)-ene. The biomarker fingerprints and petrographic based indices show that the majority of the xylite rich, matrix and sapropelic coals and shale originated from mixed forests, formed by arborescent and herbaceous communities, aquatic plants and macrophytes, under wet and slightly dry and slightly oxic–anoxic conditions.

96/04506 EXAFS characterization of iron species loaded on coal char

Five Tertiary deposits in the Czech Republic were studied using coal petrological and organic geochemical methods. Coal samples were chosen to cover four lithotypes: xylite rich coal, matrix coal, liptobiolith, and sapropelic coal. Xylite rich and matrix coals are characterized by higher ulminite and densinite contents, and lower textinite and resinite contents. Sapropelic coals from the North Bohemian and Žitava basins are formed by large amount of ulminite and densinite, and a high proportion of liptodetrinite, sporinite and alginite that prevails in sapropelic shale from the Uhelná relic. The essential difference between sapropelic coal and liptobiolith coal consists of high contents of liptodetrinite, bituminite, resinite, inertinite, and lower contents of clay minerals in liptobioliths. The biomarker composition of the aliphatic fraction includes n-alkanes, and their distribution varied according to coal lithotype: long n-alkanes were dominant in liptobioliths, sapropelic coals and shale, the mid-chain n-alkanes prevailed in xylite rich coals, and the short-chain n-alkanes were abundant in matrix coals. The prevalence of diterpenoids represented by phyllocladane type compounds indicated the presence of gymnosperm vegetation. Molecular indicators for angiosperms, present mainly as oleanenes, were also recognized in the lignite samples. Hopanoids were represented mainly by 17α(H),21β(H)-homohopane and hop-17(21)-ene. The biomarker fingerprints and petrographic based indices show that the majority of the xylite rich, matrix and sapropelic coals and shale originated from mixed forests, formed by arborescent and herbaceous communities, aquatic plants and macrophytes, under wet and slightly dry and slightly oxic–anoxic conditions.

96/04114 The effect of coal lithotype grindability and char development on pulverized fuel combustion

96/04114 The effect of coal lithotype grindability and char development on pulverized fuel combustion

96/03487 Determination of forms of organic sulfur in coal by step-wise oxidation with perchloric acid-ferric perchlorate mixture

Sr geochemistry in coal has been studied on the basis of its distribution in 457 samples of coal, coaly shales and mineral interlayers from several Bulgarian coal deposits. Model experiments were also carried out. The analysed Sr contents are lower than the average values for coals. Only the Burgas deposit is enriched in Sr due to marine influence. The coal lithotypes liptain, vitrain, xylain and fusain are usually enriched in Sr as compared to the whole samples from which they were separated.Sr occurs in both organic (Srorg) and inorganic (Srinorg) forms. The relation to organic matter is demonstrated by: (1) Sr enrichment in low-ash coals and in lighter specific gravity fractions; (2) leaching of Sr bound to humic acids by treatment with 2% NaOH; (3) sorption experiments on xylain at pH 4-5.5 - up to 92% of Sr in solution was taken up by the sorbents; a mechanism of cation exchange as well as formation of metallo-organic complexes is proposed. Host minerals of Srinorg are aragonite, gypsum, calcite and feldspar. The highest Srinorg content is related to aragonite.

Sequence stratigraphic analysis and the origins of Tertiary brown coal lithotypes, Latrobe Valley, Gippsland Basin, Australia

The methods of sequence analysis have been applied to the onshore Gippsland Basin and in particular to the Latrobe Valley Group coal measures which include up to five coal seams each exceeding 100 m in thickness. The methods appear to provide new depositional concepts to the evolution of these seams, and the development of coal lithotypes. In the eastern half of the Latrobe Valley evidence for marine transgressions into the coal measures are recorded in most of the interseam sediment splits by the presence of contained foraminifera and dinoflagellates. To the west (inland) these splits pinch out into continuous coal. However, they can be followed westwards as enhanced organic sulphur levels along sharply defined boundaries between light coal lithotypes below and dark coal lithotypes above. The dark lithotype immediately overlying each of these boundaries contains the highest sulphur value and warmer climate pollen assemblages (Sluiter et al., 1995, this volume). Colorimeter and lithotype logging strongly supports an upwards lightening cyclicity to coal colour at 12–20 m intervals through the approx. 100 m thick seams, with cycle boundaries defined at sharp planar to undulating surfaces. The lightening upward lithotype cycles together with their unique boundary conditions (i.e. enhanced organic sulphur levels, warm climatic indicators and laterally equivalent marine clay splits) are interpreted as parasequences and parasequence boundaries respectively. Each major coal seam can comprise up to five parasequences and is interpreted to represent deposition during an outbuilding high stand systems tract at one of several maximum periods of Tertiary coastal onlap. The top of each major seam shows evidence of truncation (erosion?) on a regional scale and these surfaces are interpreted to represent the sequence boundaries. The major seams are usually conformably underlain by marine clays and extensive aquifer sands, being deposits of the late transgressive systems tracts. The low stands and early parts of the transgressive systems tracts appear not to be represented in the Latrobe Valley due to its (more) basin margin location, but are probably present down-dip in the equivalent marine facies of the Seaspray Group. Stratigraphic correlation of the sequence boundaries identified in the coal measures to the adjacent, internationally dated marine Seaspray Group, provides a basis for chronostratigraphic correlation of the coal successions to the coastal onlap charts of Haq et al. (Exon Mesozoic-Cenozoic chronostratigraphic chart, version January 1988, and August 1989). From this dating it appears that each major seam is confined to high stands of third order eustatic cycles. It therefore follows that the lithotype cycles (parasequences) that comprise each seam are related to fourth order eustatic cycles. By analogy all the coal cycles may have developed under subtropical conditions as ombrogenous forested peat swamps in a similar manner to the Holocene, though tropical, swamps of Indonesia.

Investigation of low-temperature autooxidation processes in bituminous coal lithotypes

The kinetics of autooxidation processes in sub-bituminous (vitrain and clarain) and high-bituminous (clarain) coal lithotypes has been calculated by the method of Coats and Redfern. The differences in the E a values of the thermooxidative processes show structural changes in the investigated lithotypes. Their macerallar compositions and the temperature affect the reactivity of the coal samples during oxidation by atmospheric oxygen. The results obtained suggest differences between the mechanism of the autooxidation processes occurring both in the homogeneous lithotype vitrain and in the heterogeneous clarain of equal coalification degrees, and between the clarain samples of various coalification degrees.

Biogeographic, ecological and stratigraphic relationships of the Miocene brown coal floras, Latrobe Valley, Victoria, Australia

Palaeobotanical studies of the brown coal deposits of the Latrobe Valley have contributed significantly towards an understanding of the age of the deposits, existing climatic conditions and detailed depositional environments. This paper re-assesses some past reconstructions for the Early to Mid Miocene coals using recent information on plant distributions and their bioclimatic significance and on a marine incursion model for coal lithotype formation. The brown coal flora is composed overwhelmingly of rainforest taxa that presently cover a range of different environments within the Australasian region. The application of a bioclimatic prediction model to these taxa allows the construction of consistent and quantitative estimates of climates during coal-forming phases. It is considered that rainfall in the area was more than twice the 850 mm received today, with significant seasonal variation. The mean annual temperature estimate of about 19°C, indicating a mesothermal or subtropical environment, is some 2–5C higher than present and higher than previous estimates. It does, however, correspond with sea-surface temperature estimates for the Southern Ocean at this time. The original model of lithotype formation, which suggests that lithotypes conform to a successional sequence from open water in the lightest coloured lithotypes to raised bog in the darkest lithotypes, is considered to be inconsistent with the evidence for lightening upwards sequences within the coals, a central feature of the proposed marine incursion model of coal formation. The two models are reconciled to some degree by a reinterpretation of the palaeobotanical data and by the postulation of climatic rather than autogenic successional control over lithotype formation.

The coal-bearing, Cenozoic As Pontes basin (northwestern Spain) : geological influence on coal characteristics

Lignite deposits in the Cenozoic As Pontes strike-slip basin (northwestern Spain) were formed as a function of specific paleoclimatic conditions and tectonic evolution of the basin. During the early evolutionary stages, the presence of active normal faults and thrusts inside the basin resulted in two subbasins with distinct differences in sedimentary records, with respect to lignite seam occurrence, thickness, areal extent and lithotype development. In contrast, during the late evolutionary stages the basin was not split and a more homogeneous sedimentary record in terms of coal seam occurrence and lithotype characteristics developed. A total of 26 lignite samples, distributed along the basin infill, were analyzed by organic petrography and geochemistry. All are lignite B (ASTM). The lignites deposited during lower basin infill sedimentation (units l and 2) are dark, matrix-rich, mainly huminitic brown coals, with minor bright, liptinitic-rich coal lithotypes. The dark huminitic coals in these units show sedimentological and paleontological evidence of lacustrine influence. Persistent, relatively moderate to low Tissue Preservation Index (TPI) values and high average Gelification Index (GI) values are characteristic of these limno-telmatic coals. Lignites in the upper basin infill (Unit 4) are almost exclusively matrix-rich, huminitic brown coals. Persistent, widespread, low TPI values and variable, but low, average GI values are also characteristic of these telmatic coals. The overall coal petrological data trend (TPI, GI and widespread development or absence of liptinite-enriched lignite layers) recorded from the lower to the upper basin infill units agrees with the stratigraphic and sedimentological data, which show a trend of increasingly drier conditions. Development of bright, liptinite-enriched lignite layers was widespread during the early basin evolutionary stages and was influenced by punctuated water-table oscillations. Sedimentological, petrological and organic geochemical data point to the conclusion that, although the paleoenvironments where peat deposition took place did not undergo dramatic changes, they were affected by distinguishable variations (i.e., water hydrochemistry and groundwater-level stability), linked mostly to the evolution of basin morphology (depending mainly on tectonics) and basin water balance.

Paleoecology of the Fire Clay coal bed in a portion of the Eastern Kentucky Coal Field

Vertically continuous increment samples of the Fire Clay coal bed (mid-Middle Pennsylvanian, late Westphalian B), collected from a portion of the Central Appalachian Basin, were studied palynologically, petrographically and geochemically in order to partially reconstruct the paleoecology and processes associated with peat formation in the ancient Fire Clay paleomire. Results indicate that four compositional groups can be identified. They are: (1) a Lycospora—vitrinite dominant group, characterized by high percentages of Lycospora and vitrinite macerals and generally low, but variable ash yields and sulfur contents; (2) a mixed palynoflora-high vitrinite group that petrographically is similar to group 1 except that it contains a more diverse palynoflora; (3) a mixed palynoflora-moderate/low vitrinite group characterized by various admixtures of lycopsid, fern and calamite miospores, increased percentages of liptinite and inertinite macerals, and low ash yields and sulfur contents; and (4) a mixed palynoflora-high ash yield group characterized by high percentages of small lycopsid, fern, and occasionally calamite and cordaite miospores, high liptinite and inertinite contents, high ash yields, and moderate to high sulfur contents. The Fire Clay coal bed contains a distinctive flint clay parting of probable volcanic origin that naturally divides the bed into two benches. These two benches, (upper and lower), are highly disparte in occurrence, appearance and composition. In the study area the lower bench generally is thin (< 0.5 m), laterally discontinuous and mainly composed of dull (mainly durain) coal lithotypes. Ash yields typically are high; sulfur contents generally are moderate to high. Compositional group 4, the mixed palynoflora—high ash yield group defines all of the increments examined from the lower bench. In contrast, the upper bench is thick (> 0.75 m), laterally continous and mainly comprised of bright (mainly clarain) coal lithotypes. Overall ash yields and sulfur contents for this bench are generally low, although vertical variation is apparent. All of the compositional groups occur in the upper bench; in some columns, notably those that are thick and uninterrupted by clastic partings, groups 1 and 4 often occupy basal coal layers and groups 2 and 3 occur in higher layers. Other columns, especially those taken in areas of thin (< 0.5 m) Fire Clay coal, are dominated by groups 1 and 4.

N.m.r. investigation of low-rank coal lithotypes pretreated with NaH

NaH pretreatment was applied to the low-rank coal lithotypes xylain, humovitrain and humoclarain, with the aim of partial destruction of the coal structure. The treated lithotypes were fractionated according to their solubility in decalin, alkali solution, and tetrahydrofuran. The soluble fractions were analysed by 1H and 13C n.m.r. spectroscopy in solution. 13C CP-MAS and TOSS n.m.r. spectroscopy were applied to solid-state fractions. Similar structural features were observed for the decalin-soluble fractions, indicating that the different lithotypes contain considerable amounts of organic material similar in origin and degree of chemical alteration. In humovitrain alkali- and tetrahydrofuran-soluble and -insoluble fractions, altered lignin material was assumed to be the basic constituent. The xylain tetrahydrofuran-soluble fraction is considered to contain mainly resinous material, while the insoluble part is suggested as having a lignin origin. The data for the humoclarain soluble and insoluble fractions provide evidence for the significant role of lipids besides lignin in the formation of this lithotype. A cellulose component was also detected, though in small quantity. A low degree of chemical alteration is assumed for the coal matter of humoclarain.

On the geochemistry of gold in Bulgarian coals

In 10 Bulgarian coal deposits studied the content of gold varies from 3.8 to 171 ppb in ash and from 0.7 to 33 ppb in coal. For some of the deposits the sorption ash is a concentrator of gold. The coal lithotypes and especially the isolated vitrain lenses are often enriched in gold in comparision to the whole coal samples. On the basis of own data, as well as of analysed data from certain published papers the presence of Auorg (Aubio included) and Auinorg is assumed. The higher content of gold in coal of some deposits is due to the following gold-bearing source areas: the Madjarovo gold field (for the Vâlče Pole coal deposit), gold-bearing quartz veins (for the Meden Buk deposit), goldbearing placers (for the Pernik coal basin) and the influence of the marine transgression (for the Burgas basin).

Differentiation of German Tertiary brown coal lithotypes (‘amorphous’ and ‘woody’ kerogens) using ruthenium tetroxide oxidation and pyrolysis-g.c.-m.s.

Two physically separated, co-existing lithotypes of German brown coal (a structured ‘woody’ and an ‘amorphous’ lithotype) were subjected to ruthenium tetroxide (RuO 4) oxidation and pyrolysis-g.c.-m.s.. Both techniques provided results that indicated quite diferent origins for the two fossil fuel types. Particularly obvious in the oxidation products were lignin-derived aromatic acids corresponding to some of the phenolic pyrolysis products (more prevalent in the ‘woody’ material) and higher plant liptinite derived acids correlating with alkene/alkane doublets in the pyrolysates (more prominent in the ‘amorphous’ sample), reflecting these differences.

Differentiation of Victorian brown coal lithotypes as revealed by thermally desorbable biomarkers

TD/GC/MS analyses of a profile of Victorian brown coal lithotypes are reported. Specifically, weight loss on TD, triterpenoid and diterpenoid hydrocarbons, and trimethylnaphthalene isomers are considered as lithotype differentiators. In this initial use of biomarkers released by thermal desorption to characterise lithotypes, evidence is reported for differences in angiosperm/gymnosperm contributions, variations in higher plant inputs and for distinct variations of bacterial biomass content of the liththotypes. Trimethylnaphthalenes also differentiate coal seams in the samples reported in this study.