Medium Volatile Bituminous Coal Research Articles

Assessment of elements, speciation of As, Cr, Ni and emitted Hg for a Canadian power plant burning bituminous coal

Abstract A detailed assessment of elements was carried out at a power plant rated at 150 MW burning western Canadian medium volatile bituminous coal with an ash content of 34 wt.%. The distributions of elements of environmental concern (As, Cd, Cr, Hg, Ni and Pb) in feed coals, ashes, and stack-emitted materials were determined using NAA, ICPES and ICP-MS, GFAA for Pb, and CVAA for Hg. The speciation of As, Cr, and Ni was examined using XANES spectroscopy. The results show that the elements in the feed coal are within the same range for As, Hg and Pb and higher for Cd, Cr and Ni compared to other Canadian feed coals and within range for world coals. The combination of a Mechanical Cyclone Separator (MCS) and Fabric Filter (FF) removes a significant portion of the elements of environmental concern, as indicated by their relative enrichment (RE) ratios greater than 0.7. The fly ash from within the FF has a higher content of elements, such as Hg (1.58 mg/kg) than the MSC (0.13 mg/kg) due its lower temperature (130 °C) and the ability for finer particles to be captured by the baghouse. Arsenic in the feed coal is dominated by arsenical pyrite and less toxic As + 5 in arsenate forms. Arsenic is very low in the bottom ash, while in the fly ash it is largely (> 90%) present as As + 5 . Chromium in the milled coal is present as Cr + 3 in association primarily with illite. This occurrence gives rise to an aluminosilicate association in ash materials, with the chromium oxidation state remaining as Cr + 3 . Nickel in both the feed coal and ashes occurs as Ni + 2 predominantly in coordination with oxygen. No evidence for carcinogenic Ni sub-sulfides was observed. Mercury is emitted from the plant at a rate of 1.8 g/h and is mostly in the form of reactive gaseous mercury, followed by elemental mercury and particulate mercury. The rates of input of elements of environmental concern, As, Cd, Cr, Hg, Ni and Pb, for this station were 10.45, 1.13, 123.3, 0.29, 36.3 and 23.1 kg/day, respectively, of which only 0.08, 0.01, 0.71, 0.04, 0.44, and 0.17 kg/day were emitted from the stack. Indicating that most of these elements (> 99%) were captured by the particulate removing devices. The concentrations of elements in the air and in the vicinity of this power plant are low or within the range of published data for ambient air in urban and rural areas.

Influence of oxidability of carboniferous coals from the Dobrudja foredeep on vitrinite reflectance

Importance of the study of the influence of coal oxidability on vitrinite reflectance (VR) as a criterion of the quality of coals and indicator of paleogeothermal regime is shown. Overview of relevant concepts demonstrates that this issue remains debatable. Carboniferous coals of the Dobrudja foredeep, which belong to the class of helitolites in terms of their microcomponent composition, were studied. They were subjected to oxidation during storage outdoors. Consequently, the VR value of high volatile bituminous (long-flame and gas ranks, according to the Russian classification) coals decreased, but this parameter remained virtually unaltered for medium volatile bituminous (fat) coals. Bulgarian researchers obtained similar results for Carboniferous coals of the Dobrudja basin represented by helitolites and mixtohumolites. In our opinion, the VR decrease in the course of coal oxidation is caused by decrease in the condensation and density of aromatic structures and increase in the share of nonaromatic carbon atoms.

Horizontal degasification and characterization of coals in the Sabinas Sub-basin, Mexico: implications for CBM production

Research Article| September 01, 2006 Horizontal degasification and characterization of coals in the Sabinas Sub-basin, Mexico: implications for CBM production Thomas Gentzis; Thomas Gentzis Search for other works by this author on: GSW Google Scholar Keith Murray; Keith Murray Search for other works by this author on: GSW Google Scholar Renee Klinger; Renee Klinger Search for other works by this author on: GSW Google Scholar Mario Santillan Mario Santillan Search for other works by this author on: GSW Google Scholar Author and Article Information Thomas Gentzis Keith Murray Renee Klinger Mario Santillan Publisher: Canadian Society of Petroleum Geologists Received: 15 Jul 2005 Accepted: 19 Jun 2006 First Online: 02 Mar 2017 Online ISSN: 2368-0261 Print ISSN: 0007-4802 © The Society of Canadian Petroleum Geologists Bulletin of Canadian Petroleum Geology (2006) 54 (3): 221–237. https://doi.org/10.2113/gscpgbull.54.3.221 Article history Received: 15 Jul 2005 Accepted: 19 Jun 2006 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Thomas Gentzis, Keith Murray, Renee Klinger, Mario Santillan; Horizontal degasification and characterization of coals in the Sabinas Sub-basin, Mexico: implications for CBM production. Bulletin of Canadian Petroleum Geology 2006;; 54 (3): 221–237. doi: https://doi.org/10.2113/gscpgbull.54.3.221 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of Canadian Petroleum Geology Search Advanced Search Abstract The Sabinas sub-basin in northern Mexico contains gassy coals in the Upper Cretaceous Los Olmos Formation, based on both historical evidence and current desorption testing. The “Double Seam” coal is present at shallow depth (<500 m), has high vitrinite content (>86 vol%), is well-cleated, shows high diffusivity [average tau (τ) value is 56 hours] and has high natural fracture permeability (>30 mD) in the minesites. The coal averages 2.2 m in thickness but has a high ash content (32 wt%). A tonstein band is present in the middle of the Double Seam, consisting of vitrinite and inertinite embedded in a matrix of fine clays and quartz. Average desorbed gas content of this medium-volatile bituminous coal 3/g). Maximum methane adsorption at an equivalent (Romax = 1.30%) is highest in Mine V (Esmeralda Mine at >9.0 cm depth of 300 m is 15 cm3/g (as-received basis; arb). Coal bed methane is mainly methane (98%) with heating value of 38.21 MJ/m3 (1026 Btu/ft3). The coal is under-pressured and reported to be dry, with possibly free gas in the cleat/fracture system and absence of discrete mineralization. In-seam horizontal drilling prior to longwall mining has resulted in the significant reduction of in-situ gas contents and in an increase of mined coal production per shift. The Sabinas sub-basin coals are suitable for a full-scale coal bed methane (CBM) development using in-seam single horizontal and multi-lateral horizontal drilling. Similarities, but also differences, exist between the Sabinas coals in Mexico and the same coals in the Maverick Basin, Texas. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

On the effects of petrographic composition on coalbed methane sorption

Abstract The effect of petrographic composition on the methane sorption capacity has been determined for a suite of coals and organic-rich shales. Subbituminous and bituminous coals were separated into bright and dull lithotypes by hand-picking. The methane sorption capacities range between 0.5 and 23.9 cm 3 /g at a pressure of 6 MPa. The low volatile bituminous Canmore coal and the anthracite sample have the highest capacities with the “natural coke” having the lowest. For low-rank coals there is no significant difference between bright and dull samples except for one coal with the dull sample having a greater sorption capacity than its bright equivalent. For higher-rank coals, the bright samples have a greater methane capacity than the dull samples and the difference between sample pairs increases with rank. The boghead coal samples have the highest sorption capacities in the liptinite-rich coals suite and are higher than subbituminous to medium volatile bituminous samples. Pore size distribution indicates that methane is held as solution gas in liptinite-rich coals and by physical sorption in micropores in liptinite-poor coals. These contrasting processes illustrate that liptinite-rich samples need to be independently assessed. The positive relationship between reactive inertinite content and methane sorption capacity occurs within the subbituminous to medium volatile bituminous coals because the reactive inertinite is structurally similar to vitrinite and have a higher microporosity than non-reactive inertinite. Reactivity of inertinite should be assessed in CBM studies of dull coals to provide a better understanding of petrographic composition effects on methane capacity.

Storage of small samples of coking coal for thermal rheological tests

A study was undertaken with the aim of finding the best practical way of storing small coal samples in a laboratory setting to limit their extent of oxidation for maintaining good thermal rheological properties. Samples of a Canadian medium-volatile bituminous coal of Cretaceous age (‘as received’ and < 0.42 mm sizes) were stored under various media (open trays in laboratory, in an oven, under water and under vacuum) and temperatures (− 15, 4, 20 and 40 °C) for up to 60 weeks. Samples were analyzed for Chemical changes including O content, O / C, H / O, H / C, Volatile Matter, and Calorific Value; Thermal Rheological changes in Fluidity, Plastic range, Dilatation, Free-Swelling Index and Alkali Light Transmittance. Coke Quality changes in Coke Cake Contraction, Coke Reactivity and Coke Strength indices as well as Coke Optical Textures were also examined. For chemistry related changes, the most obvious ones due to oxidation are in atomic oxygen, which increases, and calorific value, which decreases. Concerning thermal rheology changes, fluidity and dilatation were found to decrease the most whereas Free-Swelling Index and Alkali Light Transmittance do not appear to be sensitive indicators of early stages of oxidation for the examined coal. Pertaining to coke quality, coke cake contraction remains essentially unchanged, Coke Strength after Reaction decreases and Coke Reactivity Index increases, and textures reveal a significant increase in coke inerts. This work has found coal oxidation to be mainly influenced by the storage temperature, with rate of oxidation increasing with temperature, and to a lesser extent by particle size, with oxidation being more likely the smaller the particle size. Of the different storage conditions tested in this investigation, keeping coal at cold temperatures (< − 15 °C) was found to be the most favourable for limiting its oxidation and thereby maintaining good thermal rheological properties.

Determination of the Effect of Different Additives in Coking Blends Using a Combination of in Situ High-Temperature 1H NMR and Rheometry

High-temperature 1H NMR and rheometry measurements were carried out on 4:1 wt/wt blends of a medium volatile bituminous coal with two anthracites, two petroleum cokes, charcoal, wood, a low-temperature coke breeze, tyre crumb, and active carbon to determine the effects on fluidity development to identify the parameters responsible for these effects during pyrolysis and to study possible relationships among the parameters derived from these techniques. Positive, negative, and neutral effects were identified on the concentration of fluid material. Small positive effects (ca. 5−6%) were caused by blending the coal with petroleum cokes. Charcoal, wood, and active carbon all exerted negative effects on concentration (18−27% reduction) and mobility (12−25% reduction in T2) of the fluid phase, which have been associated with the inert character and high surface areas of these additives that adsorb the fluid phase of the coal. One of the anthracites and the low-temperature coke breeze caused deleterious effects to a lesser extent on the concentration (7−12%) and mobility (13−17%) of the fluid material, possibly due to the high concentration of metals in these additives (ca. 11% ash). Despite the high fluid character of tyre crumb at the temperature of maximum fluidity of the coal (73%), the mobility of the fluid phase of the blend was lower than expected. The comparison of 1H NMR and rheometry results indicated that to account for the variations in minimum complex viscosity (η*) for all the blends, both the maximum concentration of fluid phase and the maximum mobility of the fluid material (T2L) had to be considered. For individual blends, two exponential relationships have been found between the complex viscosity and the concentration of solid phase in both the softening and resolidification stages but the parameters are different for each blend.

Polymeric dispersants for coal–water slurries

The effect of several low molecular weight polymers (MW < 100,000) on the surface properties of a medium-volatile bituminous coal in concentrated aqueous suspensions was investigated through adsorption, flotation, electroacoustic, and rheological measurements. The dispersing capabilities of the tested polymers, i.e. polystyrene sulfonate, humic acids, carboxymethyl cellulose, dextrin, hydroxyethyl cellulose, and hydroxypropyl cellulose depend not only on their ionic/nonionic character but also on the ability to increase the wettability of the coal surface. The anionic polymers (carboxymethyl cellulose, polystyrene sulfonate, and humic acids) adsorb less densely on the coal surfaces compared to the nonionic ones. Despite the lower adsorption density, the anionic polymers are much stronger coal dispersants since their action is a combination of steric and electrostatic repulsive forces. In contrast, the nonionic cellulose ethers can act only through steric effects. Good coal dispersants are also strong flotation depressants. The poor dispersing performance of hydroxypropyl cellulose correlates well with the inability of the polymer to depress the natural floatability of the bituminous coal. The results are discussed in terms of the extended Deryaguin–Landau–Verwey–Overbeek theory of colloid stability. The data demonstrate that rendering the coal particles hydrophilic is the common mode of the dispersing action of both anionic and nonionic polymers.

The use of sulfur to extract hydrogen from coal

Abstract The world's recoverable coal reserves contain about 3 × 10 10 tons of hydrogen. The reaction of sulfur vapor with medium-volatile bituminous coal produces hydrogen sulfide in yields up to 97% (based on sulfur), and utilizes 70–75% of the hydrogen from the coal. The conversion of hydrogen sulfide to hydrogen can be effected through commercially proven processes; several laboratory-scale processes could also be scaled up for future use. The solid by-product of the coal–sulfur reaction meets or exceeds specifications for fixed carbon, ash, and friability of conventional metallurgical coke, though produced at lower temperatures than typical by-product coke ovens. A conceptual process is presented in which sulfur is converted to hydrogen sulfide by reaction with coal, the hydrogen sulfide in turn is converted to the desired hydrogen and to sulfur, and the sulfur is recycled through the reactor. The by-product is a good quality coke, but may also have other applications as a carbon material.

Influence of coal forced oxidation on technological properties of cokes produced at laboratory scale

The effect of coal oxidation in air at 140 °C on the technological properties of cokes obtained at laboratory scale from two medium volatile bituminous coals has been studied. The proximate and ultimate analyses do not show important changes with coal oxidation time. However oxidation clearly has a strong effect on the plastic properties of the coals in view of the fact that the Gieseler fluidity eventually disappears. From this point variations in plastic properties can still be detected by FSI. Other changes, such as a shortening of the length of the saturated fragments of the aliphatic chains, a decrease in the aliphatic hydrogen content and an increase in the oxygen-containing groups are detected by PA-FTIR. It was also found that the main coke quality indices (mechanical strength and reactivity to CO 2) of both coke series are impaired with coal oxidation. A close relationship between reactivity to CO 2 and the micropore specific surface area of the cokes has been corroborated.

Petrographic and geochemical characteristics of organic matter associated with stream sediments in Trail area British Columbia, Canada

Abstract Fifty-six samples of stream sediments from 12 creeks in the vicinity of Trail, British Columbia, Canada were examined to determine their origin, characterize their organic matter and their relation to natural/geogenic and anthropogenic sources. The samples were initially screened by Rock-Eval® 6 pyrolysis for their TOC, HI, and OI contents and then examined by both reflected (polarized) and fluorescent light microscopy. It was found that organic matter in stream sediments is mostly from natural/biological sources from local vegetation, such as woody tissue, suberin, spores, and pollen, as well as altered natural/biological input from char formed due to forest fires. Anthropogenic organic matter, mostly coke particles, was also found in the stream sediments. The coke particles have anisotropic properties with medium grained texture formed from medium volatile bituminous coal. The occurrence of coke particles is limited to Ryan Creek located close to an area were some small gold, nickel, and lead smelting operations previously occurred. There is no evidence to indicate that the coke particles found in the creek are emitted from the lead and zinc smelter currently in operation in the area. There are no coal-bearing strata in the area that may have a direct input of coal fragments in any of the creeks.

Effect of coal weathering on technological properties of cokes produced at different scales

The effect of weathering (natural oxidation) on the technological properties of cokes obtained at three different scales (laboratory, pilot plant and semi-industrial), from two medium volatile bituminous coals stored at INCAR open stockyard for several months, has been studied in this work. The results show that the procedure developed at laboratory scale is useful for studying the evolution of coke quality because the trends of the main quality indexes (mechanical strength and reactivity to CO 2) are in agreement with those of the cokes produced at larger scales. Furthermore, it was found that the total porosity and the micropores specific surface area of the cokes vary with the scale of carbonization, and that they increase as follows: semi-industrial<pilot plant<<laboratory. All of which are related to the evolution of the mechanical strength and reactivity to the CO 2.

Characterization of Sulfur Functionalities of Supercritical Extracts from Coals of Different Rank, Using Reductive Pyrolysis

The extracts obtained via supercritical fluid extraction (SFE) from three Polish coals of different rank, using toluene, toluene/2-propanol, and toluene/tetrahydrofuran (THF) mixtures, were subjected to reductive pyrolysis to determine their organic sulfur functionalities. The extraction yield was in the range of 11.4−43.1 wt %, depending on the type of solvent and coal. Toluene gave the highest extraction yield for medium-volatile bituminous coal, whereas a toluene/2-propanol mixture was the most effective in the case of lignite. The organic sulfur content in the resultant supercritical extracts amounted to 2.17−3.70 wt %. The atmospheric-pressure−temperature-programmed reduction technique coupled with potentiometric detection of H2S (AP-TPR) and mass spectrometry (AP-TPR-MS) were applied to monitor the sulfur-containing compounds. During this reductive pyrolysis, these compounds were hydrogenated to H2S at specific and discrete temperature intervals. The H2S AP-TPR recovery for supercritical extracts wa...

Study on Organic Sulfur Functionalities of Pyridine Extracts from Coals of Different Rank Using Reductive Pyrolysis

The organic sulfur functionalities in the pyridine extracts obtained from lignite (lignite A), subbituminous coal (subA), and bituminous coal (mvb) were studied by atmospheric pressure-temperature-programmed reduction (AP-TPR) method. The extraction yield was in the range of 6.7-29.3 wt % with a maximum for medium volatile bituminous coal. The H 2 S AP-TPR recovery for the pyridine extracts was relatively low, not higher than 45%. The coupling of the AP-TPR reactor with a different detection system from potentiometric one, i.e., with a mass spectrometer, enables the detection not only of H 2 S but also of other sulfur-containing compounds, which were released in the volatile products during reductive pyrolysis. Alkanethiols, thiophene, and its C 1 -C 2 alkylated derivatives were detected in the volatiles. Both the char and the tar produced during an AP-TPR experiment were also studied by atmospheric pressure-temperature-programmed oxidation (AP-TPO) to monitor the sulfur compounds left and captured in the AP-TPR solid and liquid residues, respectively. The obtained extracts were characterized by high sulfur content, 1.18-3.74 wt %. The organic sulfur functionalities distribution of the pyridine extract reflects the rank of coal subjected to extraction. The AP-TPR analysis showed that for the extract from lignite thiols, alkyl and alkyl aryl sulfides dominate, whereas for the extract from subbituminous coal a comparable proportion of alkyl and alkyl aryl sulfides and thiophenes is found. Thiophenes are the major organic functionalities in the pyridine extract from bituminous coal.

Tracing the Origin of Unburned Carbon in Fly Ashes from Coal Blends

This study shows the utility of optical microscopy to trace the origin of unburned carbon in fly ashes from coal blends. Coal blends currently burned in four power groups in Spain have been investigated. Mill samples were separated into size fractions, and petrographic analysis were performed to assess the extent of blend components segregation as a function of different coal grindability. Strong segregation was observed when coals from a wide rank interval were ground together. In this case, anthracite particles accumulated in the largest size fractions, high and medium volatile bituminous coals accumulated in the smallest ones, and semianthracites accumulated in the intermediate size fractions. No clear segregation trend was observed for anthracites ground together with an inertinite-rich semianthracite. Chars from single coals were prepared in a drop tube furnace operated at 1300 °C under 5% oxygen in a nitrogen atmosphere. Petrographic analysis of chars were based on the optical texture and developmen...

Photoacoustic FT-IR study of weathered stockpiled coking coals

The process of weathering (natural oxidation) of two medium volatile bituminous coking coals stored at the INCAR open stockyard for several months has been studied by means of Gieseler plastometry, the free-swelling index (FSI) test, and by photoacoustic Fourier transform infrared spectroscopy (PA-FT-IR), the latter technique allowing only the surface of the sample exposed to the atmosphere to be analyzed. The proximate and ultimate analysis of the coals did not reveal any significant changes in their chemical composition. The Gieseler maximum fluidity (MF), however, was found to decrease with weathering time; using PA-FT-IR, a reduction in the aliphatic hydrogen content and a shortening of the alkyl chains was also detected. In addition, changes in the proportion of the oxygen-containing structures were observed, although the evolution of this kind of groups with weathering time was dependent on the raw coal.

Co-combustion of coal and tire residuein a pilot plant: A simplified modeling approach for scale-up predictionsof char oxidation

Experimental and modeling investigations have been performed on the co-combustion of a traditional fossil fuel and a tire residue. The experimental runs have been carried out using a pilot-scale vertical furnace (0.5 MW) with a burner for pulverized solid fuels. Different conditions have been set up for the co-combustion of a medium volatile bituminous coal and a tire residue. The scope was to test the feasibility of burning secondary fuels (biomasses and residues) with coals using a low NO x burner developed for pulverized coal in the ENEL Research Centre. A co-combustion model was developed for interpreting the results and extrapolating kinetic parameters to practical conditions. It considers the effect of the particle size distribution, the different reactivity, and, in general, the different combustion behavior of each fuel fed to the furnace. The kinetic scheme adopted is simple and the introduced assumptions allow easy coupling with computational reactive fluid dynamic codes. Fuel conversion, oxygen concentration and carbon-in-ash profiles have been computed and compared with the experimental results. Quite good agreement has been obtained, allowing kinetic information to be used in more comprehensive descriptions of full-scale systems.

Controls on methane sorption capacity of Indian coals

Details of methane sorption properties of some Indian coals ranging in rank from high-volatile bituminous C (0.62% Ro max) to medium-volatile bituminous coal (1.46% Ro max) were investigated to determine the major factors influencing gas adsorption capacity and desorption rate. Variables studied included moisture content, mineral-matter content, rank, and coal type (maceral composition). Adsorption isotherm analysis of dry coals showed that adsorption capacity followed a second-order polynomial trend with rank. Equilibrium moist samples showed a linear increase in adsorption capacity with rank and had a significantly reduced adsorption capacity compared to the dry coals, with the reduction being related to the moisture content. Mineral matter acted as a simple diluent to the gas adsorption capacity of the coals and was found to be nonadsorbent. Adsorption capacity (moist) was reduced by 0.32 cm3/g (10 ft3 gas/t) for every 1% increase in the ash yield. Bright and dull coal lithotypes showed strong separation in their adsorption capacities on an as analyzed basis, with the bright coals adsorbing greater quantities of gas. On a dmmf basis, however, no relationship was observed between coal type and gas storage capacity. Comparison of maceral composition with adsorption capacity (dry) confirmed this observation. Effective diffusivity (De) of methane through the coal was seen to be affected by coal type and rank. Effective diffusivity, De, decreased as rank increased, which is related to the increasing microporous nature of the coal. Bulk coals tested had 2-3 times larger effective diffusivities than bright coals, and dull coals had intermediate rates. The larger De values for the bulk coals may be related to the presence of collodetrinite coupled with mineral matter, which acts as higher permeability pathways for the gas compared with the high-ash dull coals dominated by inertinite macerals. Differences were noted with similar-age (Permian) Australian coals, where methane adsorption capacities were larger and coal type had a stronger influence on adsorption capacity. (Begin page 202)

Development and scale-up of a gas-promoted oil agglomeration process for coal beneficiation

The important characteristics of a gas-promoted oil agglomeration process for cleaning coal particles in an aqueous suspension were determined. Numerous agglomeration tests with scale-model mixing systems of different sizes with controlled amounts of air were conducted. The tests were conducted on high- and medium-volatile bituminous coals using either i-octane or hexadecane as an oily agglomerant. The performance of the system was characterized by employing the minimum time required to produce spherical agglomerates (tE), the mean agglomerate diameter (dp), coal recovery and product ash content. Among these parameters, tE was found the most useful. It is a key parameter in the scale-up of an agglomeration mixing system. This parameter was found to depend on a number of system and operating variables. By controlling these variables and conducting further agglomeration tests with mixing systems that varied in size, an appropriate size scale-up rule was established.

A study on thermal and electrical characterization of Barapukuria coal of northwestern Bangladesh

The thermal and electrical studies on the recent discovery of Barapukuria coal of northwestern Bangladesh have been carried out to elucidate the characteristics of this shallow basin coal. In addition to that electrical study, proximate analyses were performed using standard methods for rank classification. Coals are found to have low moisture, low ash, medium–high volatile matter and high calorific values and on the basis of that coals are classified as mixture of medium and high volatile bituminous coal. The dc electrical resistivity has been determined as a function of applied voltage, thickness and temperature using the ASTM standard (D 257-78) methods. For voltage variation measurement from 0 to 200 V both lump and powder compact disc samples were used. The lump samples cut parallel and perpendicular to the bedding planes were used to specify the basic structural unit (BSU) of the micro domains. It is observed that variation of resistivity is not highly affected by voltage but trend to decrease. The resistivity increases as the thickness increases and resistivity is greater when the sample oriented perpendicular to the bedding plane than that of samples oriented parallel to the bedding plane, which implies that the coals are electrically anisotropic. The results obtained have been found very similar to those of some Indian, USA (Illinois basin) and USSR (Lisichansk) in terms of their electrical characteristics. The temperature variation resistivity study reveals that the Barapukuria coals are mostly semiconductor in nature.

Adsorption and gas transport in coal microstructure: investigation and evaluation by quantitative X-ray CT imaging

Natural gas (methane) production from coal seams is recognized as one of the valuable energy sources due to high storage capacity of coal to store gas at low pressures. It is known that coal composition, pore structure, and mineral matter properties affect both the amount of adsorbed quantity and kinetics of adsorption when the coals are considered for natural gas production or mediums for storing gas, mainly methane or carbon dioxide Experiments in the field of adsorption equilibrium and dynamics usually investigate the adsorption properties on crushed coal samples within a certain range of particle sizes. This data can be used to obtain an average behavior representing the very heterogeneous coal–gas system. But, although individual pores are not likely influenced by crushing, this process destroys the natural integrity and continuity of the porous medium and mixes all the lithotypes and minerals in the same batch. This makes it impossible to investigate and differentiate the behavior of different microstructures and lithotypes. In this study, gas transport and adsorption were investigated on a 3.8-cm diameter core of a medium volatile bituminous coal from Gelik seam in the Zonguldak Basin (Northwestern Turkey) by using quantitative X-ray computerized tomography (CT) imaging technique to visualize the interior of the coal during the experiment. Coal was subjected to time-varying xenon (although not a perfect analog for methane, it provides good contrast under X-rays) gas pressure for the experiment. Adsorbed amounts at different locations were determined by scanning the coal at different times. Qualitative CT images and quantitative image data were used to investigate and compare the regions where gas is transported and stored as well as the rate of adsorption at different regions having different pore structure, and composition. The SEM and CT imaging techniques used in this study enabled us to investigate the coal microstructure falling into macropore range (>1 μm with SEM and 0.3135 mm with CT). This study clearly demonstrates that, for the specific coal sample and xenon gas conditions, different structures (in the length scale given above) and lithotypes have different adsorption capacity and rate behavior. SEM images were also used to define the regions showing different adsorption behavior.