High Inertinite Content Research Articles

Microfacies and petroleum properties of coals as revealed by a study of North Sea Jurassic coals

The influence of the composition and microstructural aspects of coal microfacies on petroleum properties were investigated in light of petrographic and geochemical studies. The first study concerns a collection of North Sea Jurassic coals of various maceral compositions. The second study is a pyrolysis-gas chromatography study on pure microlithotypes from a similar French Jurassic coal. The results show that hydrocarbon potential is logically increased by a high content in liptinite but more often in hydrogen-rich vitrinite. In the same way, the hydrocarbon potential is reduced by a high inertinite content, mainly due to pre-sedimentary oxidation of the original biomass, but also due to early diagenetic processes that lead especially to the formation of micrinite, or to post-sedimentary alterations. These trends indicate that total hydrocarbon potential is increased by an autochthonous origin of the organic matter that was deposited in a relatively closed paleoenvironment and, thus, protected from detrital and organo-detrital inputs. Finally, the oil potential of humic coals, as determined by open pyrolysis-gas chromatographic studies, as related to the weight of rock, is similar to classical source rocks. The structural aspects of the coal microfacies, which probably play a role in the release of oil from coal seams in natural conditions, are also discussed.

Sedimentological and petrographical characteristics of Cretaceous strandplain coals: a model for coal accumulation from the North American Western Interior Seaway

Coal seams formed on many Cretaceous wave-dominated strandplain sediments in North America are characterized by great lateral continuity (tens to hundreds of kilometres), substantial thicknesses (up to 12 m), relatively low ash and sulphur contents. The coals formed behind an active shoreline in areas undergoing subsidence due to shale compaction and dewatering. The zone of peat accumulation was remote from the shoreline and storm/tidal inundations and generally protected from fluvial flooding. If the rate of subsidence was too great, lakes formed and peat did not accumulate. Statistical evaluation of petrographic properties, by correspondence analysis, of the Lower Cretaceous coals show that the strandplain coals form distinctive petrographic groups that are characterized by relatively low vitrinite contents and high inertinite contents. Semifusinite and inertodetrinite dominate in the inertinite maceral group. Liptinite contents are negligible. Tissue Preservation Indices and Gelification Indices indicate for the strandplain coals a forest-type paleodepositional environment in which a relatively low water table allowed the accumulation of oxidized and partly oxidized components (fusinite and semifusinite). Significant amounts of detrital components, such as inertodetrinite and vitrinite B, are diagnostic that some transportation of the organic material took place prior to deposition. Comparison of coal facies and depositional environments from Permian coals of Australian show that the Lower Cretaceous strandplain coals have petrographic similarities to coals that were formed under regressive back-barrier conditions in the Permian. Due to differences in nomenclature, previously interpreted regressive back-barrier environments may be similar to the strandplain environments discussed here.

An appraisal of coal petrographic facies in Lower Gondwana (Permian) coal seams of India

Petrographic facies in Lower Gondwana coals of India are characterized by coal types that depend upon the paleogeographic and tectonic framework of the coal basins, paleoclimate, the flora and fauna of the coal-forming swamps, and coal-constituent characteristics. An appraisal of coal petrographic facies of these coals was made using these parameters. With time, Permian coal (peat) seams were deposited in India over a wide range of structural and sedimentary settings and formed suites of composite genetic coal types or, in other words, petrographic facies controlled mainly by temporal, climatic and floristic differences. At the first level of resolution of petrographic facies variation, the composite genetic coal types were controlled by stratigraphic sequences namely Karharbari, Barakar, and Raniganj Formations. Then, within the coal of each stratigraphic units, further differentiation in coal facies are discernible based on petrographic types in terms of restricted paleoenvironmental and structural setting. The coal seams of the Karharbari Formation are mainly characterized by high inertinite content although several local seams with high vitrinite content are present. In contrast, Barakar and Raniganj coal seams are generally characterized by high vitrinite content, although some coal seams are rich in inertinite content. The four main petrographic coal facies found in Permian strata are: (1) fusic, rich in inertinite group macerals over vitrinite; (2) trimaceric, rich in vitrinite group macerals over inertinite macerals (‘vitro-fusic’); (3) trimaceric, rich in inertinite-group macerals over vitrinite and liptinite (‘fuso-vitric’); and (4) vitric, rich in vitrinite-group macerals. The succession of these four main petrographic facies with time was governed mainly by changes in climate and peat-forming floras and paleoenvironmental conditions in the coal swamp. Petrographic composition differs within a restricted period of time as illustrated in the model given for the Bokaro coal basin. Such petrographic coal types forming coal-facies character are mainly controlled by the regional tectonic and sedimentary framework. A considerable diversity and overlapping of coal petrographic facies is discernible with most of the coal measures of India. Yet, the main petrographic facies or composite genetic coal types were controlled by evolving flora and changing paleoclimatic patterns. The delimitation of various petrographic facies of the Indian coal seams has implications for understanding the origin and evolution of Gondwana coals.

Effects of the properties and composition of coal blends on coke mechanical properties

Previous publications indicate that the mechanical properties of metallurgical coke made from coal produced in the Ostrava-Karviná coal basin are significantly influenced by the coal mass properties—atomic ratio ( H O at ), vitrinite reflectance (% R̄ov) and inertinite content (% I). In the range of lower rank (0.80–1.25% R̄ov), the size of the H O at parameter, closely associated with fluidity, is of principal importance. Laboratory, pilot-plant and full-scale experiments with coke-oven charges prepared from these coals confirm that the above statement also holds in the case of coal blends. The results obtained enable one to estimate approximately the mechanical properties of cokes produced from blends of lower-rank coal components. Low- and high-rank coals may be added to a charge in the quantity dependent on the size of the H O at parameter of the blend. In stamped charging the adverse effects—low values of the H O atomic ratio, high inertinite content, low or high values of the rank of components—are less apparent than in top charging. Metallurgical coke of satisfactory properties may also be obtained from a blend with as much as 50% inertinite content.

Petrographic Analyses of Knobloch Coal Seam (Paleocene), Powder River County, Southeastern Montana: ABSTRACT

A single core of Knobloch coal from Powder River County, southeast Montana, was drilled to obtain samples for coal quality studies. The coal occurs in the lower Tongue River Member of the Paleocene Fort Union Formation. The Knobloch coal core (63 ft long) was divided into 1-ft increments and analyzed using chemical and petrographic methods. Definite variations in maceral content were seen. Preliminary studies show relationship between ash, gelinite, inertinite, and humodetrinite contents. A zone of low gelinite, low humodetrinite, and high inertinite, located in the lower quarter of the seam, implies a period of severe oxidation occurred, possibly as swamp fires. Four zones of high inertinite and high humodetrinite (three in the upper half and one in the lower half of the seam) indicate fluctuations in the water table, allowing moderate oxidation and weathering of plant material and subsequent mechanical reworking of humic grains. Near the center of the seam, a zone of high inertinite, high humodetrinite, and high ash content suggests water levels were high enough to allow significant sediment influx as well as reworking of the humic materials. These conclusions suggest the Knobloch coal is autochthonous and hypautochthonous in origin, a result of several water-table fluctuations and/ormore » climatic changes due to drought.« less

Proposal for coal classification

Several critiques to the ‘International Classification of Hard Coals by Type’ (ECE, Geneva, 1956) have been made in the past and a revision of its usefulness is currently being carried out by several investigators. The principal drawback of this classification is that it is not applicable to coals of variable maceral composition, especially those displaying a high content of inertinite. Furthermore, the parameters hitherto used in the International Classification and in some other national systems to define degree of coalification (rank), i. e. volatile matter and calorific value, are dependent on variable maceral composition. On the other hand, the parameters used in the International Classification to determine the agglutinating and coking properties of coals are competing parameters, instead of following a hierarchy. The proposed classification scheme is based on two primary parameters determined with microscopic techniques: (1) mean maximum reflectance of vitrinite, which is a good single measure of rank; and (2) petrographic composition (vitrinite and exinite) as an indication of the type of coal. A third parameter is chosen to qualify the different classes of coal: volatile matter for anthracitic coals; dilatation for semianthracitic and bituminous coals; and calorific value for subbituminous coals and lignites. The scheme is expressed by mean of a code number of four digits, which refers to the rank (first digit), type (second and third digits) and qualification (fourth digit) of coal.

Possibilities of the utilization of micropetrographic parameters in the scientific classification of bituminous coals

Proposals for new scientific classifications of bituminous coals are based on micropetrographic parameters, i.e. vitrinite reflectance as a criterion of the coalification and maceral composition, presupposed to express the connection between the genetic peculiarities and physical, chemical, and technological properties of the coal mass. In the case of coals with high inertinite contents, however, the utilizability of these parameters meets with difficulties resulting from the subjectivity of determining the different transitional material and from insufficient knowledge of inertinite behaviour at higher temperatures. In the case of the maceral-variable bituminous coals produced in the Ostrava-Karviná Coal Basin, these insufficiencies are not important since it is especially the expression of the variability of the properties of isometamorphic vitrinites, which has decisive effects up-on the course of the thermo-chemical transformations, that is of principal importance to the scientific classification of these coals. In the first approximation, the properties of isometamorphic vitrinites may be expressed by the parameter (H/O) at, closely connected with fluidity. While the micropetrographic parameters reflect in particular the peculiarities in the chemical structure of the aromatic parts of coal macromolecules, the parameter (H/O) at expresses the properties of the non-aromatic structures of vitrinite, significantly affecting the course of its thermal degradation. The experimental results show that the value of the parameter (H/O) at, fluidity and the course of degassing the coal of a lower coalification are independent of the maceral composition and vitrinite reflectance; also that the caking and coking properties of low-rank coals are especially dependent on the parameter (H/O) at and partially on the micropetrographic parameters. All these facts should be taken into consideration in preparing new scientific classifications of bituminous coals.

Fusibility of ash from coals of the United States

A char morphology system is outlined, based on the physical and optical characteristics known to influence the burning of pulverized coal. Application of the system to high temperature char has established links between coal microlithotype predecessors and char types for subbituminous and bituminous coals. Quantities of high density and thick-walled char produced by pyrolysis at 1500 °C correlate with quantities of high density char in combustion residue, and with unburnt carbon content in fly ash for seven Australian energy coals. The proportions of different pyrolysis char types produced by any coal are shown to depend on coal rank, petrographic composition, maceral fusibility, and possibly ash content and composition, Quantities of high density chars in combustion residue can also be related to petrographic properties, including infusible inertinite content and percentage of microlithotypes of high inertinite content. Vitrinite reflectance is found to be a good parameter to differentiate burnout performance of coals with significant differences in rank. By comparing the proportions of high density, thick-walled pyrolysis char that form at 1500 °C, an estimate of burnout behaviour based on the combustion characteristics of char is obtained. Study of char types remaining after combustion also indicates potential for improvement of burnout performance, based on knowledge of the nature and origin of the unburnt carbon particles.