Claus Diessel

A char morphology system with applications to coal combustion

Abstract 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.

On balanced and unbalanced accommodation/peat accumulation ratios in the Cretaceous coals from Gates formation, Western Canada, and their sequence-stratigraphic significance

Coal composition was investigated by means of photometric and maceral analyses on closely spaced lithotype-based strip samples over the full thickness of several paralic coal seams from the Cretaceous Gates Formation of the Western Canadian Sedimentary Basin. The aim of this investigation was to test various methods of identifying accommodation trends in coal and use them to refine sequence-stratigraphic interpretation of continental sediments. Conventional sequence stratigraphy derives its subdivisions and significant surfaces from the records left by relative sea-level oscillations. These records either do not project into the continental realm, or are difficult to recognise in clastic non-marine sediments. Paralic coal seams have been selected to study this problem, because they are not entirely removed from marine influence and, compared with most inorganic deposits, coal has stored a greater wealth of information that can be analysed at a higher level of resolution. The study has led to the identification of five new surfaces with chronostratigraphic potential in the sequence-stratigraphic analysis of non-marine sediments. Two of these surfaces, called paludification surface (PaS) and terrestrialisation surface (TeS), occur at the bases of the investigated coal seams, while two other surfaces, referred to as non-marine flooding surface (NFS) and give-up transgressive surface (GUTS), form the tops of the coal. The fifth and probably most important new surface, called the accommodation-reversal surface (ARS), is independent of any particular facies and may either coincide with some of the other surfaces or occur separately. The proportion of detrital minerals has been used as the chief discriminator between different mire types and accommodation trends. Other useful indicators of mire type and peat dispersal have been the proportions of sporinite and inertodetrinite, as well as some derived maceral and/or mineral ratios, e.g., the groundwater influence index and the tissue preservation index. Isometamorphic variations of telovitrinite reflectance and fluorescence, as well as their coefficients of variation were also found to contribute to the identification of cyclic shifts between balanced and unbalanced accommodation/peat accumulation ratios. Some of these cycles, which are backed up by clastic stratigraphy, appear to correspond to the development of shallowing-upward and deepening-upward parasequences. Superimposed high-frequency, low-amplitude perturbations in the coal cycles relate to smaller-scale accommodation cycles of sub-parasequence level, not always recognised in non-marine strata. These sub-parasequence coal cycles do not always continue the shallowing-upward trend typical of conventional parasequences. Several coals were found to contain stacks of small-scale cycles with upward increasing accommodation signatures either in their lower or upper halves, or over the whole seam section.

Isometamorphic variations in the reflectance and fluorescence of vitrinite; a key to depositional environment

Abstract Petrographic investigations of serial ply samples from five high- to medium-volatile bituminous coal seams from Australia (4) and Canada (1) reveal substantial in-seam variations in the reflectance and monochromatic microfluorescence intensities of the maceral subgroup telovitrinite. The variations consist of one case of reflectance enhancement and fluorescence suppression, and four cases of reflectance suppression and fluorescence enhancement. The single case of reflectance enhancement and fluorescence suppression is due to the oxidation of the vitrinite nuclei at the sequence boundary between the Bayswater and Upper Wynn seams in New South Wales. The four cases of reflectance suppression and fluorescence enhancement result from the syn- and epigenetic absorption by the vitrinite nuclei of hydrogen donated by, presumably, anaerobic bacteria-generated lipids. Two of the coals are marine-influenced: the Liskeard Seam from the Bowen Basin by combined syngenetic and epigenetic effects, and the Greta Seam from the Sydney Basin mainly by epigenetic contact with sea water. For both coals, the results are strong vitrinite reflectance suppression and fluorescence enhancement. The remaining two coals, the Bulli Seam from the Sydney Basin and a coal seam from the Gates Formation in British Columbia, show moderate epigenetic effects on the optical properties of telovitrinite by fresh-water. In the Bulli Seam which was studied in two adjacent localities, the reflectance suppression and fluorescence enhancement of telovitrinite are stronger under sandstone roof than under shale roof. In some cases, the epigenetic effects are superimposed on syngenetic telovitrinite reflectance and fluorescence variations resulting from the cogeneration and mixing of different telovitrinite precursors, for example, autochthonous roots and hypautochthonous or allochthonous shoots. A measure of the degree of dispersal and mixing is the coefficient of variation of telovitrinite reflectance and/or fluorescence. This coefficient correlates well with detrital minerals and dispersed macerals, e.g., inertodetrinite and, to a lesser extent, sporinite. Some comments are made on slitted so-called pseudovitrinite which is regarded as a telovitrinite that was subjected to very weak post-coalification desiccation and possibly oxidation without losing much of its thermoplastic properties.

Carbonization reactions of inertinite macerals in Australian coals

Abstract Widespread disagreement about the degree of reactivity of the inertinite group of macerais is related to variations in experimental conditions of assessment and failure to appreciate technological modifications imposed on similar macerals by dissimilar source materials and depositional conditions. This has resulted in the constant under-estimation of the coking potential of post-Carboniferous inertinite-rich coals by predictive methods developed for vitrinite-rich Carboniferous coals. Coking tests up to 1000 °C have been carried out on 20 coals of different rank in such a manner that coked portions of the samples could be correlated with their uncoked equivalents. It has been found that an inverse relationship exists between the level of precarbonization reflectance (PCR) of inertinite and the reflectance and bireflectance of its coke. The increase in the latter parameter is non-linear and involves a sudden jump which is taken as the boundary between reactive (high bireflectance) and non-reactive (low bireflectance) inertinite. In relation to coal rank a reactivity field for inertinite has been delineated which can be subdivided into two areas of high and moderate reactivity, respectively. On the whole, the proportion of reactive inertinite is larger than allowed for in most petrography-based coke stability calculations.

The cold-climate origin of inertinite-rich Gondwana coals

Abstract In the inertinite-rich Permian coals of Australian there occurs a close association between inertodetrinite and alginite of a kind which has been generally overlooked in the past. The association is believed to be a consequence of the environment of deposition and especially the climate, which is inferred to have been one of wet, cool summers and freezing winters. The inertodetrinite formed by drying out of a gelified, homogenised precursor; the algae lived at the periodically desiccated surface of the accumulating peat. Much of the evidence for these conclusions has come from the combined use of light microscopy and transmission electron microscopy.

High-resolution sequence-stratigraphic correlation between shallow-marine and terrestrial strata: Examples from the Sunnyside Member of the Cretaceous Blackhawk Formation, Book Cliffs, eastern Utah

The Sunnyside Member of the Upper Cretaceous Blackhawk Formation in the Book Cliffs of eastern Utah provides an ideal opportunity to investigate high-resolution sequence-stratigraphic correlation between shallow-marine and terrestrial strata in an area of outstanding outcrop exposure. The thick, laterally extensive coal seam that caps the Sunnyside Member is critical for correlating between its shallow-marine and terrestrial components. Petrographic analysis of 281 samples obtained from 7 vertical sections spanning more than 30 km (18 mi) of depositional dip enabled us to recognize a series of transgressive-regressive coal facies trends in the seam. On this basis, we were able to identify a high-resolution record of accommodation change throughout the deposition of the coal, as well as a series of key sequence-stratigraphic surfaces. The stratigraphic relationships between the coal and the siliciclastic components of the Sunnyside Member enable us to correlate this record with that identified in the time-equivalent shallow-marine strata and to demonstrate that the coal spans the formation of two marine parasequences and two high-frequency, fourth-order sequence boundaries. This study has important implications for improving the understanding of sequence-stratigraphic expression in terrestrial strata and for correlating between marine and terrestrial records of base-level change. It may also have implications for improving the predictability of vertical and lateral variations in coal composition for mining and coalbed methane projects.

Fluorometric analysis of inertinite

Abstract In coal petrology, fluorescence microscopy has mainly been used in the study of liptinite (exinite) macerals. Recently, its scope of application has been widened to investigate vitrinite. This paper describes the conditions under which inertinite can also be studied by fluorometry. The method makes use of relatively long-wave excitation. Although the strongest signals are received through a green exciter filter at 546 nm, blue light excitation (450–490 nm) is preferred because the fluorescence spectrum is broader, the microscopic image more polychromatic and maceral identification is easier compared with longer-wave excitation. Inertinite macerals are divided into fluorescent and non-fluorescent constituents on the basis of both visual distinction and relative intensity determinations at 650 nm measuring wavelength. It appears that fluorescent inertinite corresponds closely to reactive fractions determined by previous coking experiments.

Coal and coke petrographic investigations into the fusibility of Carboniferous and Permian coking coals

Abstract For the purpose of conducting coal/coke mass balance calculations ten Australian coals of Permian age and twenty Carboniferous coals from the Ruhr district of Germany have been carbonized, and both feed coal and coke samples have been subjected to petrographic and other laboratory analyses. The results demonstrate that inertinite dissociates thermally into four components: (1) gas and liquor; (2) fused coke matrix (FCM); (3) partly fused coke inclusions (PFCI); and (4) unfused coke inclusions (UFCI). Fluorescence intensity measurements offer the best means of identification of the boundaries between the above groups and, in doing so, divide coal components into fusible, partly fusible and infusible constituents without the need to refer to any maceral classification. Fluorescence intensity cut-offs for the three solid categories have been determined. They correspond to 3% 1 650 w for FCM/PFCI and 1.5% for PFCI/UFCI.

Stratigraphic Style of Coal and Non-Marine Strata in a High Accommodation Setting: Falher Member and Gates Formation (Lower Cretaceous), western Canada

ABSTRACT The Lower Cretaceous Falher Member and Gates Formation of the Western Canadian Sedimentary Basin provide an opportunity to investigate high resolution stratigraphic correlation in non-marine to marginal marine rocks. This is due to the large volume of high-quality data available from subsurface cores and wireline logs in the Elmworth area, corresponding outcrops in the adjacent Rocky Mountains foothills, and outcrop and continuous core data from the Bullmoose Mine area in northeastern British Colombia. A key component of the high resolution interpretation and correlation in this region is the abundant, thick coal seams that occur in fresh mine highwalls and also in cores from the mine sites and the Elmworth area. Using coal petrographic constituent analysis and derived parameters, we are able to identify systematic variations in coal properties that respond to changes in accommodation. In particular, these properties enable us to distinguish two types of peat (transgressive and regressive) characterized by wetting- and drying-upward behaviour linked to variations in the groundwater table. They also enable recognition of a range of non-marine stratigraphic surfaces that record responses to changing accommodation, including accommodation reversal surfaces, flooding surfaces, hiatal surfaces, paludification surfaces and terrestrialization surfaces. A combination of these coal parameters, together with the facies characteristics of the surrounding non-marine and marginal marine rocks, enables recognition of distinctive high-resolution stratigraphic signatures in the rocks. This in turn provides a previously unavailable ability to correlate stratigraphic unit from their downdip marine position, through the shoreline zone and into the terrestrial realm. For the Falher/Gates unit, we recognize nine regionally correlatable cycles over a vertical distance of around 300 m and a lateral distance of 80 km downdip and 150 km along strike. The basis for this detailed correlation is the similarity of the accommodation trends as seen in both the organic and clastic facies. Results show that earlier concepts of parasequences and their flooding surface boundaries in marine rocks need to be significantly modified in the terrestrial realm. Sharp hiatal parasequence boundaries in the marine realm such as flooding surfaces and wave/tidal ravinement surfaces may correlate updip to packages of rocks that pass gradationally from transgressive to regressive units and preserve the transitions between the two. Non-marine sediments may accumulate during and following shoreline regression, and prior to and during shoreline transgression. The exact style and preservation of the non-marine stratigraphic package depends on the local balance between accommodation and sediment flux at the time of deposition. Coals occur in both regressive and transgressive styles and may initiate or terminate parasequences. Coals may also occur as compound coals that span more than one parasequence and contain internal discontinuity surfaces. End_Page 275------------------------

Comparison of two petrographic methods for determining the degree of anomalous vitrinite reflectance

Abstract Three Australian Permian bituminous coals from well-documented geological settings chosen to cover a range of rank, and orthohydrous, subhydrous and perhydrous vitrinite compositions, were used to compare and contrast two petrographic methods for correcting anomalies in vitrinite reflectance (VR) due to compositional variation. One of the methods (fluorescence alteration of multiple macerals (FAMM™)) is based on the fluorescence alteration properties of coal macerals, and the other on paired measurements of reflectance and fluorescence intensity. The methods are only applicable to fresh (unoxidised) coals or dispersed organic matter (DOM). Both methods use a reference ‘normal’ orthohydrous telovitrinite line on which results from perhydrous or subhydrous samples are projected to obtain the equivalent reflectance of orthohydrous telovitrinite. The results of the two methods on the test samples are similar but they differ in detail.