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.     

The char structure characterization from the coal reflectogram

Coal is a heterogeneous substance and its heterogeneity is identified and characterized by variation in reflectance. The main objective of this paper is to characterize the heterogeneity of char and to correlate it with the coal reflectogram, which accounts for both rank and maceral composition effects. Chars from two density fractions in a set of coals were obtained in a Drop Tube Furnace (DTF) at 1400 °C in N₂ environment. The chars were examined under a Scanning Electron Microscope (SEM) and the morphology information was obtained from the image-processing technique. The average porosity of char changes systematically with the FMR of its parent coals (defined as the summation of each reflectance multiplied with its frequency). The char porosity increased with an increase in FMR up to a critical value around 98. With further increase in FMR, the corresponding char becomes dense. The char macro porosity distribution was found to be related to the coal reflectogram. In general, the char porosity distribution shows two peaks, which corresponds to the inertinite and vitrinite peaks in reflectogram. The intensity depends on the maceral content. The relationship between the char porosity and coal reflectance for this set of sample has been found, which is strongly dependent on the coal rank. However, these findings cannot be applied to coals with a strong maceral association (microlithotype).     

Dynamic nuclear polarization 13C n.m.r. of coal

A novel n.m.r. method for determining the aromaticity of coal has been evaluated. Polarization transfer from the paramagnetic electrons is used to enhance the intensity of the ¹³C n.m.r. spectrum. Analysis of five samples of Gondwana bituminous steam coals shows that the aromaticity of inertinite is far greater than that of vitrinite and that variation of maceral composition is a major factor determining coal aromaticity. This has been confirmed by the study of maceral concentrates.     

Coalification paths of exinite,vitrinite and inertite

Coalification is a burial metamorphic process fundamental to understanding the origin and nature of coals and petroleum. Accurate assessment of Coalification requires removal of the variation in coal properties owing to differences in coal type. This is best achieved by assessing the coal rank of the maceral groups exinite, vitrinite and inertinite (and ultimately the macerals within each group) in terms of maximum reflectance. The mean maximum reflectances of exinite (R?_E max), vitrinite (R?_v max) and inertinite (R?_I max) are highly correlated over the rank range, soft brown coals to low-volatile bituminous coals. A single exinite Coalification break is identified at 0.4 to 0.5% R?_V max. Thereafter, exinite coalification occurs at an increasing rate (R?_E max relative to R?_V max) over the rank range 0.5–2.0% R?_V max, crossing the vitrinite Coalification path at 1.55% R?_V max. A phase of rapid inertinite Coalification (0.7–2.0% R?_I max) occurs between 0.2 and 0.9% R?_V max. Since exinite is a major land-plant source of hydrocarbons, and R?_E max is a sensitive indicator of organic maturation over the range 0.2–1.1% R?_E max, which corresponds to the main phase of oil generation, R?_E max can be a most useful indicator of petroleum generation. The inertinite lnkohlungsprung represents a dramatic compositional change which should be taken into account when considering the origin of inertinite, its utilization properties and the general processes of rank change and organic maturation.     

炼焦煤煤化度表征的研究

对8组挥发分相同或接近的不同矿点炼焦煤进行了实验,分别测定了8组煤的煤岩组分和镜质组平均最大反射率、软化起始温度,通过对比分析可知:具有相同或相近挥发分的煤,由于煤岩组分的差异,镜质组平均最大反射率的差值达到0.03%~0.24%;并不是惰质组含量的差值越大,镜质组平均最大反射率的差值就越大,惰质组含量差值8%~9%的炼焦煤,镜质组平均最大反射率的差值几乎一致。建议炼焦企业尽可能通过镜质组平均最大反射率来认识炼焦煤的煤化程度,从而提高煤质技术理论水平。     

Photoacoustic microscopy of coal macerals

Photoacoustic microscopy, in which laser-light energy absorbed by coal macerals is converted into thermal energy, has recently emerged as an in-situ technique for coal maceral characterization. By employing two possible detection modes, different thermal properties can be measured and correlated with the material properties of the coal macerals. For the piezoelectric detection method, the photoacoustic signal is proportional to $\text{aB}\text{pc}$, where a is the coefficient of thermal expansion, B is the bulk modulus, p is the mass density, and c is the specific heat capacity of the maceral. The second method employs a gas microphone where the photoacoustic signal is proportional to $\text{l}\text{√Kpc}$, where K is the thermal conductivity. Photoacoustic data gathered by both methods on vitrinite and pseudovitrinite macerals from Appalachian basin coals agree with values predicted from known values of a, B, p and c. Data indicate that the thermal-elastic and thermal-conductance properties vary in a systematic manner from low- to high-rank coals. Throughout the entire rank range up to 92% carbon, vitrinite exhibits a significantly different photoacoustic response than pseudovitrinite. The photoacoustic measurements reflect the chemical composition and molecular structure of the individual coal macerals.     

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.     

煤岩显微组分分离富集物热化学反应特性

依据煤中不同类型有机质性质差异对其进行分离，进而分质利用是实现煤炭清洁高效利用的有效手段。论文利用重选法将一种低变质烟煤分质得到镜质组较原煤48.25%增加至76.02%的富镜样，惰质组较原煤43.96%增加至63.98%的富惰样，以及矿物质含量高于61.99%的富矿样。利用热重-质谱分析仪，考察了分离富集物的热解反应特性及气体逸出规律，及其燃烧和气化反应特性。结果表明，分离所得富镜样热解反应失重量及热解过程中逸出的小分子挥发分的量及组成与富惰样和富矿样均有明显差异，表明分质实现了煤中不同类型官能团的分离富集。而由分离所得富镜样、富惰样和原煤热解失重峰温基本一致则表明分质所得煤的主体官能团结构仍较为接近，但含量有明显差距。富镜、富惰与原煤的燃烧曲线整体趋势较为类似，燃烧活性差别不大。以气化反应峰值温度高低判断，富镜样气化反应活性最低，富惰样与原煤气化反应活性较为接近，富矿样气化反应活性最高。将原煤在对应热反应时的理论反应曲线与实验曲线进行对比，发现煤分质过程及煤中镜质组、惰质组和矿物质的分离与否对热解过程挥发分的逸出影响较小，但导致了其燃烧和气化反应活性有所降低。     

Thermochemical properties of coal fractions of different density: A review

Research is reviewed regarding the composition and thermochemical properties of coal fractions of different density. The properties discussed are the thermogravimetric parameters; the free-swelling index; the plastic-layer thickness; the dilatometric characteristics; the yield of fluid (mobile) components of the plastic mass. These properties are determined by the petrographic (maceral) composition of the fractions. With increase in density of the fractions, the liptinite and vitrinite content declines, while the inertinite content grows. Consequently, the chemical structure becomes less aliphatic and more aromatic, with corresponding deterioration in thermochemical properties of the fractions. The results show that fractionation of the coal prior to processing is potentially very effective.     

Composition, structure, and properties of Donetsk Basin and United States coal of the same metamorphic stage

The composition, structure, and properties of Donetsk Basin and United States coal of the same metamorphic stage are compared. The samples represent coal from the whole metamorphic series, with vitrinite reflection coefficient R _o = 0.7?C1.8%. Separate regression equations for Donetsk Basin and United States coal describe the relation between the composition (C ^daf , H ^daf , O ^daf ), structural characteristics (C_ar, f _a, ??, and B) calculated from the elementary composition, the technological properties (V ^daf , y, Q _s ^daf ), and the vitrinite reflection coefficient. Significant differences are found in these properties for Donetsk Basin and United States coal of the same metamorphic stage. These differences are mainly due to the different degrees of reduction of the coal. With a vitrinite reflection coefficient up to 1%, the degree of reduction is greater for United States coal than for Donetsk Basin coal. With greater metamorphic development (R _o ?? 1.0%), Donetsk Basin coal is characterized by even lower degrees of reduction.     

Properties of high ash char particles derived from inertinite-rich coal: 1. Chemical,structural and petrographic characteristics

An investigation was undertaken to determine the properties of high ash coal–chars derived from South African discards rich in inertinites, for the development of suitable overall reaction rate models at low temperatures (<900 °C). Detailed characterisation results of the parent coal and chars prepared at 700 °C and 900 °C obtained from standard coal analytical methods, petrographic techniques, CCSEM image analysis and a surface adsorption method are presented. The parent coal consisted of 32% by volume of inertite (“pure” inertinite), 7% of vitrite (pure “vitrinite”), and 13% of bi- and tri-macerite, 30% of maceral/mineral mixtures (carbominerite) with 18% of mineral-rich material. Reflectances obtained from measurements taken on vitrinites and total maceral reflectance scans increased dramatically on charring at 900 °C and were accompanied by an extension of vitrinite reflectance class distributions indicating higher molecular ordering. Volatiles were liberated essentially from the original parent vitrinites, creating fine gas pores. Inertinites increased in reflectance but not in porosity and were characterised as dense char fractions in the final charred product, according to a coal form analysis. Structural change due to low temperature thermal stress fracturing (passive deflagration) occurred early on in the temperature regimes, creating increased surface areas and porosity. The chars consist of a high proportion (52%) of extraneous rock fragments together with minerals mainly as fine inclusions in carbon rich particles (13%). The chars had very low porosities and surface areas. These were created by the devolatisation of reactive maceral associations and deflagration. Such materials could introduce intra-particle diffusional effects during gasification and combustion of millimetre size particles at low temperatures.     

焦粉替代瘦煤的配煤炼焦试验研究

通过煤岩显微分光光度计系统对焦粉配煤炼焦进行了系统的研究,研究了焦粉的配入量对配合煤的镜质组最大反射率及区间变化和显微组分变化的影响,结合小焦炉产品各项质量指标的变化,得到太原煤气化公司焦化厂焦粉的最佳配入比例为1.0%～1.7%,最佳粒度范围为<3mm占98%～100%、<1mm占78%～80%、<0.2mm占40%～50%。煤岩显微分光光度计系统的应用,不但促进了焦粉回配炼焦技术更加系统和精细,也保证了在焦粉配入后焦炭质量的稳定。     

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.     

Coal enrichment with separation into fractions by density

The proposed model of the coal composition consists of formulas for the mineral component Ml and organic mass (the vitrinite Vt, inertinite I, and liptinite L maceral groups) as a function of the density ρ. The model includes differential and integral density distribution functions of the total coal mass and formulas for the coal properties as a function of the density. That permits modeling of the profound transformation of coal with enrichment and separation into fractions by density.     

Petrographic aspects of the hot strength of coke

The strength CSR of metallurgical coke after high-temperature reaction with CO₂ is determined by the depth of reaction and depends on the petrographic composition of the initial coal, the degree of metamorphic development, and the content of catalytically active ash components. Qualitative aspects of coke’s hot strength are reflected in the mathematical model, whose parameters include the vitrinite content Vt in the batch, the inertinite content I, the reflective index R _o,r of vitrinite, and the basicity index of the ash.     

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.     

The estimation of char reactivity from coal reflectogram

Measurements of the intrinsic reactivity of chars to oxygen are increasingly being sought as an indicator of the combustion potential of fuels. The coal reflectogram has been used to characterize the chemical properties of coal and its resultant char structure. In this study, six Australian coals varying in rank were separated using density separation technique to obtain vitrinite and inertinite rich fractions. Chars were obtained from these density fraction samples in a Drop Tube Furnace (DTF) at 1673 K. The reactivity of the chars was measured non-isothermally in a Thermal Gravimetric Analysis (TGA) in the temperature range of 573–1073 K. The results suggested that with the increase in the coal rank, the maximum reactivity of chars derived from vitrinite rich fractions decreases, while the reactivity of chars derived from inertinite rich fractions decreases with the increase in the inertinite content in samples and has no obvious relationship with rank. The kinetic parameters were derived using data from non-isothermal TGA after accounting for changing in surface area with conversion. The frequency factor is found to decrease with increasing coal FMR, defined as the summation of each reflectance value multiplied by its frequency, for a constant activation energy (E=146 kJ/mol). This suggests that the behavior of a maceral is characterized primarily by its reflectance distribution instead of the type of its parent coal.     

Effect of Wyodak coal properties on hydroliquefaction reactivity

The effect of Wyodak coal properties on liquefaction reactivity as measured by distillate yield and cyclohexane conversion has been investigated. Spot samples of four Wyodak subbituminous coals from the Anderson and Canyon coal seams in the Powder River Basin of NE Wyoming were liquefied in microautoclave and batch reactor experiments. Runs were made using two different Wyodak coal-derived solvents. Emphasis in this work was directed toward correlation of C₄-700 K distillate yield and cyclohexane conversion as functions of measurable physical, chemical and petrographic properties of the feed coal. Reactivity rankings were found to be the same using either measure of coal reactivity. However, the data indicated that distillate yields were a function of both solvent quality and feed coal properties. For each solvent studied, selected coal properties, including carbon content, total and organic sulphur content, vitrinite content and total reactive maceral (vitrinite plus exinite) content, were found to give statistically significant correlations with distillate production and cyclohexane conversion. Pyritic and sulphate sulphur contents did not appear to enhance liquefaction yield or conversion at the reaction conditions studied. However, any catalytic effects due to pyrite or sulphate sulphur may have been masked by the use of two high quality liquefaction solvents.     

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.