Alberta Coals Research Articles

A comprehensive experimental procedure for CO2 coal gasification: Is there really a maximum reaction rate?

A novel procedure to perform carbon dioxide (CO2) gasification studies was tested with two different Alberta coals and compared to the most common procedures using thermogravimetric analysis (TGA). The designed experiments indicate that maximum reaction rates reported in the literature were probably a consequence of the increasing CO2 concentration in the gas mixture when the inert gas was switched to CO2. It has been proven that, independent of feedstocks, the time to observe this maximum reaction rate was constant, indicating the reported maximum reaction rate depends only on the gas dispersion when the gasifying agent is fed and not on the surface properties of the char.In addition, the comparison of different experimental procedures shows the time that the char was exposed to an inert gas atmosphere prior to gasification, decreased the reactivity of the char. The reason is a reduction of the char mesopore area, which was induced when pyrolysis and gasification were separated with an isothermal step using an inert gas. The random pore model is the most common model used to describe coal and biomass gasification in the literature, since it can predict a maximum reaction rate for a determined conversion. However, its usage may be inappropriate for gasification kinetics analysis, if the changing gas mixture effect and the char surface area reduction induced by the experimental procedure are not considered.

Assessing the Water Uptake of Alberta Coal and the Impact of CO2 Injection with Low-Field NMR

Abstract Coal property characterization is an essential step to develop coalbed methane (CBM) recovery processes. In most cases, coal contains free water in the cleats (except dry coal), as well as moisture that forms an integral part of the coal structure. Most CBM production starts with dewatering coalbeds to initialize the gas recovery. Therefore, the wetting behaviour of coal by water is an important aspect in coal property studies. As CO2 has a strong affinity to coal, CO2 injection may change the coal wetting behaviour during a so-called enhanced coalbed methane process (ECBM). Studies on coal wettability are rare. This paper investigates the water uptake by Alberta coal and its wettability alteration due to CO2 injection using low-field nuclear magnetic resonance (NMR). Low-field NMR is a technique used in logging and in the analysis of fluids contained in reservoir rocks. It measures the hydrogen density in reservoir fluids and distinguishes between 'free' bulk water and 'bound' surface water. CO2 is invisible to NMR, but its impact can be detected by changes in the water signal. Experiments on coal samples in the form of dry and moist powder and chunk are used. The water uptake rate can be shown by monitoring the geometrical mean transverse relaxation time. From the spectra of different coal samples, water can be characterized into free, capillary-bound and subsurface-bound (adsorbed) water. These forms of water have different uptake behaviour inside coal. The injection of CO2 will cause coal dewatering, and the effect will increase with elevated CO2 pressure. Introduction Coalbed methane (CBM) has evolved into a commercially profitable source of unconventional natural gas. Canada has vast resources of coal and it has been estimated that the total in-place reserves are 36 ? 1012 m3. Over 60% of Canada's CBM resource is in Alberta(1). Coalbed methane has the potential of contributing a significant portion of Canadian natural gas production in the foreseen future. Using CO2 to enhance methane recovery has been discussed by several researchers(2, 3). This process is called CO2-ECBM. If successful, its implications include CO2 sequestration in deep unmineable coalbeds. Coal property characterization is an essential step to develop CBM/ECBM recovery processes. In most cases, coal is wet and contains free water in the cleats, as well as moisture that forms an integral part of the coal structure. Some coals found in the Western Canadian Sedimentary Basin's Horseshoe Canyon Formation are dry coals, which means the coal cleats no longer preserve free water. Most CBM production starts with dewatering coalbeds to initialize gas recovery. Therefore, the wetting behaviour of coal by water is an important aspect in coal property studies. As CO2 has a strong affinity to coal, CO2 injection may change the coal wetting behaviour in the ECBM process. Published studies on coal wettability are very rare to the best of our knowledge. Low-field NMR is a relatively new technique used in logging and in the analysis of fluids contained in reservoir rocks.

Coalbed methane resources and reservoir characteristics from the Alberta Plains, Canada

Alberta has vast coal resources that may be a potential source of coalbed methane (CBM). Exploration and research are currently underway in the province to quantify gas potential, identify key geological factors that maximize CBM potential, and identify the ‘most favourable’ areas for CBM production potential. There are four main coal zones within the Plains and Foothills of Alberta. The Ardley Coal Zone of the Plains is undergoing CBM exploration and production piloting. Much of this effort is within the west-central Pembina area. Horseshoe Canyon Formation coals of south-central Alberta were initially thought to have gas concentrations too low to be economic CBM producers. It is these coals, however, that host Alberta's first commercial CBM production project. Although similar in both geographic distribution and coal quality to Horseshoe Canyon coals, not much is known regarding the gas potential of underlying coals of the Belly River Group. The deeper Mannville coals have some of the highest gas concentrations of Alberta coals; however, they are also relatively deep and have lower permeability than the overlying Belly River, Horseshoe Canyon and Ardley coals. Maximum gas-in-place for the Plains and Foothills has been estimated to be greater than 500 trillion cubic feet (1.42 * 1013 m3). Although this number is very large, little is known as to how much of this huge resource is actually producible. A key challenge to producibility in Alberta has been the generally low permeability of coals with the highest gas concentrations (Mannville coals), and the moderate to low gas concentrations of higher permeability coals (Horseshoe Canyon and Ardley coals). Regionally, coal distribution and average gas-in-place concentrations are calculated for the Alberta Plains. Identifying and explaining local areas with favourable CBM production characteristics within the regional setting is necessary to establish economic CBM plays within Alberta. There are currently several pilots and numerous exploration efforts underway in the province to demonstrate production potential. This study integrates existing data with new data collected from key areas that show favourable CBM potential. There is great opportunity for CBM development in Alberta. Local areas have enhanced characteristics favourable to production. Ongoing geological investigations are needed to identify characteristics that will serve as an exploration tool for future CBM discoveries.

Properties of fly ash stabilized haul road construction materials

ABSTRACT Larger haul trucks are being used at surface mines in Canada thus requiring better haul roads to carry heavier loads. The availability of good quality aggregate to build haul roads is limited for prairie coal mines. However, most of these mines are located adjacent to coal-fired electrical power plants, which produce by-product fly ash as a waste. Fly ash can be used to increase strength and stiffness of soil and road bases. Unconfined compressive strength tests conducted on various mixtures of fly ash, kiln dust, mine spoil, and coal seam partings showed that the cementing characteristics of unclassified fly ash from central Alberta coals was low. However, the addition of cement kiln dust, which is high in CaO, enabled the fly ash to exhibit significant cementing action. Mixtures of fly ash, kiln dust, and mine spoil or coal seam partings had unconfined compressive strengths of about 1 MPa and elastic moduli of about 350 MPa after 14 to 28 days. This compares favourably with compacted mine spoil or coal seam partings which have estimated unconfined compressive strengths of less than 0.4 MPa and moduli of about 50 MPa. Thus fly ash stabilized mine spoil or coal seam partings were found to have potential for use in constructing haul road base and sub-base layers since maximum tire pressures on the running surface are less than 0.7 MPa.

Hydropyrolysis of Alberta coal and petroleum residue using calcium oxide catalyst and toluene additive

Hydropyrolysis of a mixture of Alberta coal and Athabasca bitumen was carried out in a batch reactor using calcium oxide as an alternate catalyst and the results were compared with those of widely used iron oxide and well-known NiMo/Al 2O 3 catalysts. Most of the reactions were done at temperatures of 500–540°C, residence time of 1 min and hydrogen pressure of 3.4 MPa. Maximum distillable oil (below 523°C) yield of 55 wt% and pitch conversion of 62 wt% were obtained in the presence of CaO or Fe 2O 3 and these values were higher than those without catalyst, although NiMo/Al 2O 3 catalyst gave much higher oil yield and pitch conversion. Catalyst concentration (above 2 wt%) has no consequence upon the distribution of various product fractions. In another study, addition of 15% toluene to the feed in the absence of catalyst led to higher distillable oil yield (68 wt%) and pitch conversion (72 wt%) in the hydroconversion of coal and bitumen mixture. Increase in toluene concentration from 15 to 50 wt% had no positive effect on the product yields.

Variation in micropore capacity and size distribution with composition in bituminous coal of the Western Canadian Sedimentary Basin: Implications for coalbed methane potential

The effects of lithotype, maceral and mineral contents on the micropore capacity and size distribution are investigated for a medium-volatile bituminous coal from the mid-Cretaceous Gates Formation of north-east British Columbia and a high-volatile bituminous coal from the Cretaceous of Alberta. Vitrinite content (vol.% mmf) ranges from 18 to 95 for the Gates coal and 36 to 85 for the Alberta coal. Ash yields (wt%) vary from 4.4 to 33.7 for the Gates coal and 1.2 to 10.6 for the Alberta coal. Dubinin-Radushkevich CO 2 micropore capacities (cm 3 g −1 mmf) measured at 273 K range from 23.7 to 43.9 for the Gates coal and 37.0 to 54.7 for the Alberta coal. Low-pressure Dubinin micropore capacities and Langmuir and BET monolayer volumes measured at 273 K generally increase with increasing total and structured vitrinite content and decrease with increasing inertinite and mineral matter content. The increase in micropore capacity with vitrinite content is due to an increase in the number of micropores, as demonstrated by Dubinin-Astakhov micropore size distributions. For the Gates suite, a sample with high total vitrinite and semifusinite contents has the largest micropore capacity, which may be due to the creation of micropore capacity in semifusinite through burning (charring). Micropore heterogeneity increases with an increase in inertinite and mineral matter content. Coal composition is important in determining the micropore capacity and size distribution and hence the gas capacity of bituminous coals.

95/05585 E.p.r. HFS spectral characteristics of Mn 2+ impurity ions in Argonne and Alberta coals

95/05585 E.p.r. HFS spectral characteristics of Mn 2+ impurity ions in Argonne and Alberta coals

Combustion Properties of Macerals from Four Alberta Coals

Abstract The combustibility of handpicked vitrinite and inertinite concentrates from four Alberta coals ranging in rank from subbituminous C to low-volatile (LV) bituminous was measured and compared with the parent coal. The combustion properties of the concentrates were studied by routine analysis of the maceral concentrates, examination of low-temperature reactivity on a thermogravimetric analyzer, examination of high-temperature burnout profiles on the entrained flow reactor, and measurement of char combustion reactivity on a single-particle combustor. The structure of partially combusted chars from two of the coals and their maceral concentrates were examined using scanning electron microscopy. Low-temperature oxidation of pyrolysis chars formed from the coals and macerals indicated that all of the samples had similar activation energies of between 29,900 and 35,600 cal / mol. For three of the coals, the inertinite char had lower reaction rates under these conditions. Under entrained flow combustion conditions at 1000°C, the subbituminous and high-volatile (HV) bituminous coals were very reactive, with 90% burnout in air in less than 0·2 s. The initial weight loss of the inertinite maceral during devolatilization was significantly less than the vitrinite maceral or parent coal for the three reactive coals. However, the chars formed from inertinite burned at similar rates to vitrinite char. The similarity in maceral char combustion rates was confirmed on a single-particle combustor; however, the three reactive coals and their macerals burned at the diffusion limit. Although char combustion rates were similar, the low initial weight loss of the inertinite fraction would result in longer combustion times for complete combustion of the inertinite char. Scanning electron microscopy revealed that inertinite chars from the HV bituminous and the LV bituminous coals generally retained their original morphology1 during devolatilization, white the vitrinite macerals went through a plastic phase. The “reactive” HV bituminous coal formed porous, spongelike chars, while the “unreactive” LV bituminous coal developed vesicular chars with low surface area.

E.p.r. HFS spectral characteristics of Mn 2+ impurity ions in Argonne and Alberta coals

A new, more comprehensive study of the 9 and 33 GHz CW e.p.r. Mn 2+ impurity ion spectral characteristics of the eight Argonne premium coals and two Alberta h.v. bituminous coals is reported. These characteristics include the HFS a 1 relative amplitude, linewidth and lineshape as well as a more accurate and reliable determination of the g-value, the HFS parameter A and the c 0 2 and c 0 4 ZFS parameters for powdered coal samples from the ΔM = ±1, Δm = 0 central and weak non-central transitions using the spin Hamiltonian diagonalization spectral simulation method of analysis. The six Mn 2+ Δm = 0 HFS central transitions observed in coal samples do not have two component resonances, unlike those for Mn 2+ in polycrystalline calcite, which is attributed to lineshape broadening. However, the a 1 amplitude and linewidth variation for the six Mn 2+ HFS central transitions observed in each of the coal samples studied is consistent with that observed in polycrystalline calcite. The consistency of the a 1 amplitude and linewidth analysis as well as of the improved values of the e.p.r. spectral parameters for Mn 2+ impurity ions in calcite and coal provides more conclusive confirmation that the e.p.r. spectrum of Mn 2+ originates from the calcite mineral component of coal.

The role of oxygen, nitrogen and argon in the low-temperature oxidation of a dried Alberta coal as studied by dynamic in situ 9 GHz CW-e.p.r.

The results are reported of a study of the changes in spin concentration and in the e.p.r. spectral parameters for the free-radical and the Mn 2 + HFS resonances observed in dried high-volatile bituminous Alberta coal samples due to low-temperature oxidation in dry air, nitrogen and argon gas flow in the interval 20–300 °C. The temperature-dependence of the free-radical resonance for air treatment differs significantly from that for nitrogen and argon treatment, but the Mn 2 + resonance is independent of the type of gas up to 190 °C. It is concluded that the low-temperature oxidation processes in coal depend critically on the presence of loosely bound water and oxygen.

Dynamic in situ 9 GHz c.w.-e.p.r. low-temperature oxidation study of selected Alberta coals: 1. Comparison of an hv bituminous and a subbituminous coal

This paper reports the results of a study of the changes in the character and spin concentrations of the free radical species present in subbituminous and hv bituminous Alberta coals caused by low-temperature oxidation whilst subjected to dry air flow in the temperature interval 20–250 °C. These results were obtained using a new experimental technique called dynamic in situ 9 GHz continuous wave-electron paramagnetic resonance (c.w.-e.p.r.) spectroscopy, which is described. The e.p.r. lineshape changes were analysed using radial difference a o d o -Argand diagrams. All the c.w.-e.p.r. spectral parameters and the spin concentrations exhibit maxima near 100 °C. The observations can be explained by the free radical involvement in the oxidation process. It is concluded from the temperature variation of these parameters and of the lineshape that two free radical species exist with slightly different g-factors and linewidths whose spin concentrations increase as the temperature rises and additional oxygen is coordinated such that the composite lineshape remains essentially constant and nearly Lorentzian. It is shown that the temperature dependence of the free radical evolution process differs significantly in the subbituminous and hv bituminous coal samples studied and that this evolution is determined by the quantity of dry air available.

The 9 and 33 GHz EPR Spectra of Mn 2+ impurity ions in polycrystalline calcite—Central transition

The 293 K EPR spectra of Mn 2+ impurity ions in polycrystalline natural and synthetic calcite and in the calcite impurity in various coal samples have been studied at 9.2 and 33.3 GHz. The spectra obtained at these two frequencies were found to differ dramatically. At 9.2 GHz, the lineshapes of the central transition hyperfine resonances are in good agreement with previous measurements. The 33.3 GHz EPR spectrum has some features which have not been reported previously at Mn 2+ concentrations below 1000 ppm. Computer simulation programs for both spin-Hamiltonian perturbation and diagonalization techniques were used to describe the mono- and polycrystalline spectra. It was found that the simulated spectrum using the spin-Hamiltonian diagonalization method agrees with previous 9.3 GHz monocrystal data within an error of 0.1 mT for the central transitions and of 0.13 mT for the noncentral transitions, whereas the simulation using the perturbation method had errors of 0.2 and 0.6 mT, respectively. An analysis of the polycrystalline hyperfine resonance lineshapes observed at 9.2 and 33.3 GHz for 1, 50, and 520 ppm Mn 2+ concentrations has been performed using both simulation methods. The hyperfine resonance lineshapes observed at 9.2 GHz are due to the magnetic field angular variation caused by the axial zero field splitting (ZFS) term C 0 2( S). The hyperfine resonance lineshapes observed at 33.3 GHz are shown to be due to the combined effect of A-tensor and g-tensor anisotropy, the axial ZFS, and the spin-spin interaction. The Mn 2+ impurity ion EPR spectrum observed in an Alberta coal and several Argonne coal samples is shown, using lineshape analysis, to originate from their calcite mineral impurity. The lineshape broadening observed in coal samples is characteristic of a strong spin-spin interaction and may be due to interactions with the free radicals and other impurity ions as well as between Mn 2+ ions.

Dynamic in situ 9 GHz c.w.-e.p.r. low-temperature oxidation study of selected Alberta coals: 2. Influence of mineral matter in an hv bituminous coal

The effect of the presence of manganese and cobalt impurity ions on the formation of free radicals in the low-temperature oxidation of an Alberta hv bituminous coal has been investigated using dynamic in situ 9 GHz c.w.-e.p.r. spectroscopy. Changes in the effective g-factor and effective linewidth ΔB 1 2 e.p.r. spectral parameters as well as in the relative total spin concentration and the lineshape were monitored in both virgin and demineralized coal samples subjected to dry air flow whilst being heated from 20 to 250 °C. The virgin sample produced a larger number of free radicals than the demineralized sample when heated. This demonstrates that the presence of transition metal ions in the mineral matter component of the virgin coal plays an important role in promoting the low-temperature oxidation process. It is shown that two free radical species are present and that the presence of the transition metal ions promotes the preferential creation of the free radical with the larger g-factor.

Dynamic in situ 9 GHz c.w.-e.p.r. low-temperature oxidation study of selected Alberta coals: 3. Influence of exinite macerals and moisture in an hv bituminous coal

Dynamic in situ 9 GHz c.w.-e.p.r. has been used to study the low-temperature oxidation in the interval 20 to 250 °C of hv bituminous coal samples enriched and depleted in exinite, when dried or moisture-saturated. The changes in the e.p.r. spectral parameters and relative total spin concentration are correlated with the maceral composition and moisture content of the samples. These parameters exhibit maxima at ~100 °C. The percentage increase in the spin concentration for dried coal samples between 20 and 100 °C is greater in the exinite-depleted than in the exinite-enriched sample. The 20 °C free radical spin concentration is higher in dried than in moisture-saturated coals but the concentration changes more rapidly with temperature for moisture-saturated samples. This observation is in a good agreement with the interpretation of the lineshape distortion changes determined using radial difference a o d o -Argand diagrams. It is concluded that the moisture content associated with the vitrinite maceral is the most important factor in determining the rate at which the low-temperature oxidation processes occur in coal.

The Mn 2+ HFS spectrum in argonne and Alberta coals at 9 and 33 GHz

The 13°C 9 GHz and 20°C 33 GHz CW EPR spectra of the Δm = 0 and Δm = ±1 HFS transitions of Mn 2+ impurity ions were observed in six Argonne premium coal (APC) samples and one Alberta by bituminous coal. The EPR spectral parameters are in good agreement with previous measurements: g av = 2.00176(30) and A av = −9.395(5) mT at 9.2 GHz; g av = 2.00138(30) and A av = −9.397(8) mT at 33 GHz. The first direct estimation of the zero field splitting parameters D and F for the APC and Alberta coal samples has been obtained using the weak HFS of the ΔM = ±1, Δm = 0 | ± 5 2 〉 → | ± 3 2 〉 and |± 3 2 〉 → |± 1 2 〉 outer transitions; the values are D = 7.88(6) mT and F = 3.2(5) μT for five of the six APC and D = 8.04(8) mT and F = 2.8(1) μT for the Alberta coal. These values confirm that the Mn 2+ ions are located in the calcite (calcium carbonate) impurity. The calcite Mn 2+ ion concentration in the Argonne premium coals and the Alberta coal were estimated. It is found that only a small fraction of the Mn 2+ concentration determined by chemical analysis for the APC samples is in the calcite impurity whereas a large fraction is present in the Alberta coal calcite component.

20 °C, 9 GHz CW-EPR saturation measurements of five selected Alberta coals

This paper reports the first determination of the spin-lattice (T1) and spin-spin (T2) relaxation times at 20 °C for two subbituminous and three hv bituminous selected Alberta coals using 9 GHz CW-EPR saturation measurements. Argand diagrammatic techniques were used to verify that the lineshapes were Lorentzian since the deviation was less than 4%. Consequently, it was assumed that the CW-EPR spectral resonances could be approximated to homogeneously broadened lineshapes and saturation techniques could be used to determine these relaxation times. The T1 and T2 relaxation times are in good agreement with values reported in the literature using saturation measurements, but two orders of magnitude shorter than those obtained using ESE because coal EPR spectral resonances are the unresolved superposition of comparatively narrow homogeneous resonances.

CO2 gasification kinetics of two alberta coal chars

AbstractCO2 gasification kinetics of chars from two Alberta coals (Obed Mountain, high volatile bituminous and Highvale, subbituminous) have been studied using a thermogravimetric analyzer (TGA) and a fixed bed reactor. Charification and gasification reactions were performed sequentially in both the TGA instrument and in the fixed bed reactor to simulate real gasifier operating conditions. TGA and fixed bed data were processed numerically to evaluate the kinetic rate of CO2 gasification of the chars. Calculated gasification kinetics could be correlated using both the volume reaction and the grain models. Activation energies of the kinetic rate constants were near 200 kJ/mol for both Highvale and Obed Mountain coal chars using the TGA data. The activation energies calculated for the Obed Mountain coal char using the fixed bed reactor were about 250 kJ/mol. For all the cases studied the calculated activation energies were nearly the same for both the volume and grain reaction models.

Regional Resource Evaluation of the Coal-bed Methane Potential in Alberta

The Alberta portion of the Western Canada sedimentary basin contains over 7.7 {times} 10{sup 12} tons (7 {times} 10{sup 12} tonnes) of coal ranging in rank from lignite to semianthracite. These coals are distributed throughout the mountains, foothills, and plains regions and range from Jurassic to Tertiary in age. Most of the coal in the plains region is subbituminous, while bituminous coals are common in the foothills and mountains. Promising geologic settings for coal-bed methane recovery are found in all three reigons. The first testing of Alberta coals for methane commenced in 1974. The Alberta petroleum industry has recently shown renewed interest, and companies have begun testing samples and acquiring land positions. Resource estimates of the coal in nontraditional mining areas are currently being revised and improved. A resource evaluation study by the Alberta Geological Survey of the coal-bed methane potential of the province has been heavily subscribed to by industry. The plains coals to a depth of about 400 m were extensively explored and evaluated by the Alberta Geological Survey in the early 1980s. The deep coal resources have received considerably less attention despite being penetrated by thousands of petroleum exploration and production wells. The currrent resource evlaution studymore » is defining hte stratigraphic and structural framework of the coals throughout the province through production of an extensive suite of cross sections and maps. Regional trends in subsurface coal ranks are being defined for the whole province for the first time by collecting hundreds of vitrinite reflectance measurements.« less

Electrochemical oxidation of acidic Alberta coal slurries

The electrochemical oxidation of four different types of Alberta coals of bituminous and subbituminous rank have been studied in 1 M H2SO4 slurries at 90°C under potentiostatic conditions at an applied potential of 1.0 V with respect to RHE. Two particle sizes (>200 and <60 mesh) were used to determine the rate constant for the electrochemical oxidation of coal mediated by Fe3+. Two rate constants,k c.1, andk c.2, representing initial (0-∼6 h) and subsequent (∼6–24 h) stages of electrochemical oxidation of coal, respectively, were observed. A correlation between the rate constants and the fixed carbon content (rank) of the coals was drawn. Gas chromatographic analysis of the gaseous oxidation products indicated the production of carbon dioxide. The rate and current efficiency for this production was determined as a function of electrolysis time with the rate of production reaching a steady-state level after a few hours of electrolysis. Possible mechanisms, for the oxidation of coal are discussed, based on structural and functional group models.

A Kinetic Study of the Electrochemical Oxidation of Alberta Coal Slurries

The kinetics of the Fe3+‐mediated electrochemical oxidation of four types of Alberta coals in acidic slurries have been investigated. A critical examination of the previously reported mechanisms and kinetic treatments for the electrochemical oxidation of coal slurries is provided. In this work, a new approach was developed to analyze and to determine the rate constant of the electrochemical oxidation of coal, shown here to be an irreversible process. Two second‐order rate constants, and , representing the initial (0 to ca. 6h) and subsequent (ca. 6 to 24h) stages of electrochemical oxidation, respectively, were obtained from this approach. A correlation between these rate constants and the fixed carbon content (rank) was observed for the coals studied.