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There has been a long history of using X-rays to visualize coal and its transitions during various treatments. Advances and improved availability has allowed the application of X-ray computed tomography (CT) to create 3D images to aid rationalizing coal behavior. This non-destructive technique has been used in the determination of mineral dispersion for coal cleaning potential; swelling/shrinking...
Coal has a heterogenous porosity that influences its specific surface area (SSA) and CH4 adsorption and desorption. However, the pore size distribution obtained with N2 adsorption is only reliable at pore sizes >2nm omitting the important contribution of micropore (<2nm). Here, 13 coal samples from three series were measured by both the N2 at 77K and CO2 at 273K, respectively, to compared the...
Here a new automated and inexpensive atomic simulation approach including sequential oxygen diffusion and simplified reaction was created to explore the char reactivity and combustion behavior during oxy-fuel combustion. Two large-scale (>40,000 carbon atoms) coal chars (higher- and lower-porosity chars) that differ primarily in pore volume and pore size distribution were evaluated against graphite...
The development of coal char structures with pyrolysis has been extensively investigated but has traditionally been focused on the carboniferous coals in the northern Hemisphere. In this investigation, the properties of pyrolysis chars generated from inertinite- and vitrinite-rich coals (81% and 91%mmb by volume, respectively) collected from selected South African coalfields were determined. Chars...
The chemical–structural properties of four South African bituminous coals were investigated using wide angle X-ray diffraction–carbon fraction analysis (WAXRD–CFA), attenuated total reflection Fourier transform infra-red spectroscopy (ATR–FTIR), solid state 13C nuclear magnetic resonance spectroscopy (ss 13C NMR), and high resolution transmission electron microscopy (HRTEM). The aromaticity of the...
The generation of coal chars is an important intermediate step in coal conversion processes such as combustion and gasification. The char structure impacts their behaviour in these processes. Detailed investigations on slow-heated coal chars utilizing molecular modelling approaches are limited in comparison to the more extensive work on coal. Also South African (SA) coal is generally not as well studied...
Enhanced coalbed methane (ECBM) can be recovered by injecting a gas such as carbon dioxide into the reservoir to displace methane. The contrast between density, viscosity, and permeability of the resident and displacing fluids affects the efficiency of ECBM recovery. The prediction of earlier breakthrough becomes complex as the permeability may vary by orders of magnitude during gas injection and...
Structural complexity and variability of the chemical properties define technological applicability of coal and demand increasing accuracy and spatial resolution from the techniques used for coal characterization for development of new, clean, and efficient technologies of coal utilization. Here, we combined spatially-resolved reflectometry, fluorescence, and confocal micro-Raman spectroscopy with...
There has been a remarkable rise and fall in the frequency of coal science related journal publications from US entities. There has been a passing of the mantle from the US to China as the leading nation for English-language coal journal articles. An ISI Web of Knowledge (using the Web of Science database) evaluation of journal articles with “coal” in the title (in English-language journals) for the...
Between 1942 and 2010 there were >134 proposed molecular level representations (models) of coal. While they spanned the rank range, bituminous representations are the bulk, with far fewer lignite, and very few subbituminous or anthracite representations. They have transitioned from predominantly 2D pen and paper drawings into 3D computational structures, and have recently increased in complexity,...
It has long been recognized that coal is somewhat aligned. Multiple techniques imply a structural alignment but its quantification has been challenging. Moreover, discrepancies exist among techniques as to whether low-rank coals are aligned. The extent of structural alignment for the rank range was quantified directly via image analysis of high-resolution transmission electron micrograph lattice fringes...
A large-scale molecular model for Illinois No. 6 Argonne Premium coal is generated based on an automated construction approach in an effort to move toward capturing the continuum structure. The model contains 50,789atoms within 728 molecules and is the largest, most complex coal representation constructed to-date. The aromatic ring size distribution was based on multiple high-resolution transmission...
Knowledge of the molecular weight distribution is important for rationalizing coal behavior. While many analytical approaches generate average data, inclusion of coal’s inherent structural diversity would improve molecular representations of coal and their usefulness. The molecular weight distribution of Pocahontas No. 3 coal was estimated based on a new approach coupling HRTEM lattice fringe image...
Two South African coals similar in rank and age, but different in maceral composition, were studied using solvent swelling. Inertinite-rich Highveld coal (dominated by semifusinite) and vitrinite-rich Waterberg coal were evaluated for swelling extent and swelling rate using N-methylpyrrolidone (NMP) and CS 2 /NMP. A stop-motion videography method was developed to study individual particle...
Molecular representations for two Permian-aged South African coals, inertinite-rich Highveld (dominated by semifusinite) and vitrinite-rich Waterberg were constructed based on analytical data. High-resolution transmission electron microscopy (HRTEM) was used to determine the size and distribution of aromatic fringes, thereby affording the base aromatic skeleton for each coal model. Sulfur, nitrogen,...
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