Heavy media separation of SRC-II feedstocks: 1. Effect on coal properties

The objectives of this investigation were to determine the effects of coal preparation on the properties of Run-of-Mine (ROM) and washed Powhatan and Ireland Mine coals and to assess the potential effects on SRC-II liquefaction yields. The effect of washing on the two coals was found to be quite similar. For both coals, the properties were altered more significantly by changes in separation media gravity than by changes in the coal size. The elemental composition of the Powhatan and Ireland washed coals was correlated with carbon content. It was shown that both the hydrogen and oxygen levels increased linearly with the carbon content of the coal samples. However, the $\text{H}\text{C}$ and $\text{O}\text{C}$ ratios were not changed significantly by coal cleaning. Only small variations in the nitrogen and organic sulphur levels were observed while the sulphate sulphur and chlorine levels were not affected by coal cleaning. The major impact of the coal cleaning was to reduce the pyritic sulphur (and hence the total sulphur) content of the coals. Most of the pyritic sulphur was shifted into the middling coal and refuse fractions while the clean coals had much lower contents and the pyritic sulphur level decreased with increasing carbon content. Coal cleaning did not significantly alter the maceral contents of vitrinite, exinite, total reactive macerals (TRM), or the reflectance of vitrinite; all these parameters varied over a very narrow range, probably within the precision of the measurement technique.     

Macerals in bituminous coals and the coking process: 2. Coal mass properties and coke mechanical properties

Bituminous coals produced in the Ostrava-Karviná coal basin show considerable variation in their maceral composition, vitrinite reflectance and fluidity. There is a close association of the latter with the $\text{H}\text{O}$ atomic ratio expressing the different chemico-structural properties of vitrinites of lower coalification. These properties of the coal mass all influence the coke mechanical properties; moreover the $\text{H}\text{O}{}_{\mathrm{at}}$ parameter is of principal importance to the course of the coking process. Laboratory, pilot-plant and full-scale experiments show that coals rich in inertinite may give cokes of suitable mechanical properties, providing the $\text{H}\text{O}{}_{\mathrm{at}}$, ratio and the bulk density are high enough. It should be noted, however, that these coals contain finely dispersed inertinite in the vitrinite mass and this may have a positive effect on the coke mechanical properties.     

Optically anisotropic fragments in a Western Canadian subbituminous coal

Large Isotropic and anisotropic, angular and rounded fragments of inertinite were found in a Canadian subbituminous coal (%R oil = 0.50). The istropic fragments included pyrofusinite, macrinite and pseudovitrinite with pre-oxidized, heat-treated fragments showing oxidation rims. The anisotropic fragments include the heat-treated residue of liptinite, e.g. resinite showing granular anisotropy, pyrolytic carbon and fragments of vitrinite showing basic anisotropy. The morphology of inertinite fragments is described and an attempt is made to correlate these particles with heat-affected coal macerals. The occurrence of pyrolytic carbon with a reflectance of 3.11% and of liptinite showing anisotropy in a coal matrix with a reflectance of 0.50% is unusual. It indicates the detrital nature of the pyrolytic carbon. The formation of isotropic and anisotropic inertinite was possibly due to a thermal event, perhaps a wood or swamp fire. The pseudovitrinite found in these coals may have been formed by heat-treatment of fossil oxidized vitrinite fragments. The anisotropic fragments in the coals (e.g. pyrolytic carbon and anisotropic vitrinite), are detrital and are grouped with inertodetrinite.     

Dependence of carbon dioxide sorption on the petrographic composition of bituminous coals from the Czech part of the Upper Silesian Basin, Czech Republic

The effect of the rank and of the maceral composition of bituminous coal on carbon dioxide sorption capacity was studied on the basis of samples from two coal mines (Darkov, ?SM) from the Czech part of the Upper Silesian Basin. The samples from the two mines cover a small but very significant section of coalification within the transition zone between high-volatile bituminous A coal and medium-volatile bituminous coal, where porosity and sorption properties pass through their minima. The coal porous system was characterized by the micropore volume evaluated using the sorption isotherm of carbon dioxide and the volumes of meso-, macro- and coarse pores were determined by high-pressure mercury porosimetry. The micropore fraction in the coal porous system ranged between 53% and 75%. It was particularly high in coals with high vitrinite content, namely collotelinite, and also in coals with high inertinite content. The carbon dioxide sorption capacity was determined from the carbon dioxide sorption isotherms measured using a gravimetric sorption analyzer at 298 K until a relative pressure of 0.015 p/p_s, and was interpreted by characteristic parameters of the Dubinin and Langmuir equations. It was found that the adsorbed amount of CO₂ in the ?SM coal increases with the content of vitrinite and collotelinite, whereas no increase or only a slight increase was observed for the Darkov coal. The tendency of adsorption capacity to depend on maceral composition, and also to some extent on coalification, observed for the ?SM coal, may be related to higher microporosity due to the coalification process or oxidative processes leading to the formation of pseudovitrinite.     

Dependence of coal liquefaction behaviour on coal characteristics. 2. Role of petrographic composition

The techniques used were the same as those used in Part 1 (p 34). Comparison of the liquefaction behaviour of two lithotypes from a Kentucky bituminous coal indicated that in this process pseudovitrinite is a reactive maceral. The hydrogenation of sets of maceral concentrates obtained from a New Mexico sub-bituminous and a Kentucky bituminous coal showed fair correlations between conversion and the total concentration of the presumed reactive macerals (vitrinite, pseudovitrinite and sporinite). Similar concentrates from a Montana lignite showed no such correlation; the one sample that showed a high conversion was a high-density fraction that had a high mineral-matter content and in which nearly all the pyrite in the coal had accumulated. Two samples that have boghead and cannel characteristics gave quite different results on hydrogenation. Both were highly aliphatic in structure and had unusually high hydrogen contents and volatile matter. One, which contained appreciable proportions of sporinite, alginite and resinite, gave essentially no conversion to oil. The other, predominantly vitrinitic but containing alginite as the second most abundant maceral, gave an excellent yield of an oil of low viscosity and aromaticity. It was concluded that although rank, petrographic composition and perhaps geological history are important factors determining liquefaction behaviour, there are other characteristics of coals that may at times override these basic parameters, and the composition of the inorganic matter may be the most significant of these other characteristics.     

Contribution of vitrinite macerals to the liquefaction of subbituminous coals

Four Alberta subbituminous coals were selected to investigate the contribution of vitrinite macerals to liquefaction. There are indications of a rectilinear correlation between conversion yields of different density fractions of coal and their vitrinite content, but it is too early to discern any conversion factor by which any maceral group may be used to predict the liquefaction behaviour of a subbituminous coal. Contrary to common belief, not all the vitrinite fraction of the feed coal is reactive. There seems to be a definite positive correlation between the percent vitrinite reacted and the liquefaction conversion yield. Much more research work is needed to further understand the contribution of vitrinite macerals to liquefaction of a subbituminous coal.     

Inert coal macerals in combustion

Pilot-scale pulverized-coal combustion experiments with two western Canadian coals have shown that the combustion efficiencies of the coals were inversely related to the inert contents of the coals, i.e. semi-fusinite, fusinite and oxidized vitrinite. These macerals were found to persist through the flame in a partially reacted form. The burn-out of a coal with an inert maceral content over 50% was unaffected by normal changes in combustion conditions; the same changes were successful in improving the burn-out of a coal containing less than 40% inert macerals. Coals with high inert maceral contents produce fly-ash with high levels of unburnt carbon and will require a combination of higher temperatures and higher excess-air levels and longer residence times to achieve combustion efficiencies similar to those of coals with higher reactive-maceral contents. The association of resinitic and bituminous materials with the mineral matter in the Canadian sub-bituminous coal indicated that macerals which contribute significantly to ignition and flame stability are discarded as a washery reject.     

Organic sulphur in coal macerals

Measurement has been made of the organic sulphur concentration in coal macerals of several bituminous coals. Variation of organic sulphur content among the several maceral types is striking. In three coals, the highest concentration of organic sulphur occurs for those macerals with a density around 1.18 gm cc⁻¹. This density corresponds to the maceral type sporinite in these coals. This finding has been verified by direct examination of the organic sulphur content of sporinite macerals embedded in whole coal.     

Coal characterisation by automated coal petrography

Automated imaging techniques were refined to characterise the rank and maceral composition of coals by a full maceral reflectogram of polished coal grain mounts. Precision was improved by processing individual grains in each image separately and correcting within the software for the topography that occurs between the different macerals and minerals in the grains. Maceral group proportions and vitrinite reflectance information extracted from these reflectograms compared well with manual results for a comprehensive suite of Australian coals varying in rank from a mean vitrinite reflectance of 0.48-2.13%. A parameter that combines rank and type calculated from the reflectograms correlated strongly with chemical properties determined by ultimate and proximate analyses. For a limited number of samples, for which coking tests had been performed, this parameter also correlated with estimated coking performance.     

Enhancement of plastic properties of inert-rich oxidized cretaceous coals via the water-gas shift reaction

In some cases cretaceous coals from Western Canada contain considerable amounts of inert components. These are of two general types: one resulting from in situ vitrinite oxidation and the other consisting of inherently inert macerals. Such oxidized inert-rich coals may be unsuitable for commercial utilization. In some combustion systems a high proportion of unburnt carbon may remain in the fly ash indicating incomplete combustion of the different macerals. In addition, carbonization and liquefaction are unfavourably affected. The development of a process strategy to permit the utilization of these coals by improvement of plastic properties via the water-gas shift reaction is described. This process is applied to the upgrading of three samples of naturally weathered inert-rich coal from Western Canada demonstrating the transformation from non-coking to coking coal.     

Retention of liptinitic structure in vitrinite chars

Liptinitic macerals in medium and low-volatile bituminous coals (C=87.9 and 90.0 wt% daf) which have undergone a plastic stage during primary carbonization (<600 °C) retain their original botanical structure. The liptinite materials retain their original identity but develop coarser grained mosaics and stronger anisotropy than the vitrinite residues of the same coal. The retention of original botanical structure in liptinitic macerals is probably attributable to their simple polymeric structure, which is different from that of the associated vitrinite and to carbonization at high heating rates (10 and 60 °C min^?1) which facilitates the development of a distinct two-phase optical texture and anisotropy in carbonized residues of bituminous coals.     

Interpretation of the chemical composition of bituminous coal macerals

Various methods of identifying and classifying macerals are evaluated on the basis of literature references and our own experimental results. Comparison of the diagrams $\text{H}\text{C}$ vs $\text{O}\text{C}$, atomic $\text{C}\text{H}$ ratio vs weight percentage of carbon, and atomic $\text{C}\text{H}$ ratio vs atomic percentage of carbon demonstrates the advantages of the characterization of maceral composition by means of the atomic carbon percentage, which is a function of the content of all five organogenic elements that enter into the composition of the combustible matter of caustobioliths. Illustration by means of maceral analyses from the same seam, of results from pyridine extraction, and of humic acid composition further confirms this view.     

Properties of vitrinite concentrates of South African coals

Low-ash vitrinite concentrates of representative South African coals have been prepared and analysed. Various properties when plotted against carbon content show inflections at $\text{1}\text{1}\text{2}$ to 2% lower carbon content than normal British coals. These differences are ascribed to the heating effects of dolerite intrusions.     

Study on the structure and gasification characteristics of selected South African bituminous coals in fluidised bed gasification

The gasification characteristics of three South African bituminous coals were investigated in a bubbling fluidised bed reactor. The three coals are similar in rank, but two are inertinite-rich coals and the third has a high vitrinite content. The microstructural characteristics of the parent coals and their resultant chars were determined using XRD, FT-IR, Raman and petrographic analysis. The microstructural changes that occurred in the organic (maceral) and the inorganic (mineral) fractions of the selected coals were evaluated. The change in the carbon structure was correlated to the proportions of inertinite and vitrinite macerals in the coals. High vitrinite content resulted in an increase in the order of the disordered carbon structure after gasification and this leads to greater graphitised ordered carbon structures. While a high inertinite content resulted in low or no structural transformation of the chemical structure. The transformation of inorganic mineral constituents of the coal was correlated to the amount of inertinite present in the selected coals. Higher proportions of inertinite macerals and inertinitic chars resulted in higher proportions of melted minerals. Char samples with low proportions of organic matter resulted in higher proportion of melted minerals covering the char surface.     

Coal flash pyrolysis: 4. Polymethylene moieties in coal macerals

An analysis for polymethylene moieties in purified coal macerals has shown the (CH₂)_n (wheren?5) content, by a liquefaction—¹ H n.m.r. method, to be highest in exinite macerals and lower in vitrinite and inertinite macerals. From any particular coal, the (CH₂)_n content of the vitrinite was higher than the inertinite but lower than the exinite. Pyrolysis of these macerals gave ethylene yields proportional to the (CH₂)_n content.     

Re-examination of the phenolic hydroxyl contents of coals

In connection with studies of the dependence of liquefaction behaviour on coal characteristics, parameters were needed that might effectively characterize the organic chemical structures. Accordingly, the phenolic hydroxyl contents of 37 coals from three geological provinces of the USA have been determined, by acetylation with ¹⁴C-labelled acetic anhydride. The results, when expressed as fractions of the total organic matter in the coals, showed a good inverse correlation with the carbon contents (dmmf). However, application of a stepwise multiple regression analysis to the data developed a linear equation relating hydroxyl content to the vitrinite reflectance, calorific value and vitrinite content, the fraction of variance explained being 92%. When the hydroxyl contents were expressed in the alternative manner, as fractions of the total oxygen content, no correlation could be seen with carbon content. However, in the wide scatter of points on the graph, the data are seen to fall into three reasonably distinct populations such that at the same level of rank, hydroxyl contents typically decrease for coals from the three provinces in the order Interior > Eastern > Rocky Mountain, implying that coals from these areas differ in structure as a result of differing antecedents. Statistical analyses showed that $\text{OH}\text{O}$ has some significance in determining liquefaction behaviour, but it is not among the coal properties found most significant.     

Conversion of caking coal into non-caking coal by treatment with sulphur and sulphur dioxide

The effects on the caking properties of coals of reaction between the coals and S₈ and SO₂, have been studied. Caking coals (Akabira, Shinyubari, Zollverein, Indian Ridge, and Big Ben) lose their caking properties when treated with S₈ above 200 °C. For Shinyubari coal the crucible swelling number decreases from $\text{8}\text{1}\text{2}$ to 2 with treatment temperature of 235°C in which 5% of S is incorporated into the coal. The decaking of coal is attributed to thio-ether cross-linkages. Caking coals also lose completely their caking property when reacted with SO₂ at 170 °C. The decaking action of SO₂ is attributed to oxidation of coal in which ether cross-linkages are formed.