Inherent Moisture Research Articles

Impact of inherent moisture on the methane adsorption characteristics of coals with various degrees of metamorphism

Gas and water coexist in coal reservoirs. Many scholars have examined the effect of moisture on the gas adsorption property of coal. In this paper, the oxygen-containing functional groups and pore characteristics of five coal samples with different degrees of metamorphism were studied by Fourier transform infrared (FTIR) spectroscopy and CO2 adsorption method, and methane adsorption tests were carried out on coal samples with different inherent moisture contents. The water-holding capacities of different rank coals are related to their oxygen-containing functional groups and micropores characteristics, and the former play a decisive role. This is probably the main reason why low rank coals have stronger water-holding capacity than medium and high rank coals. The Langmuir volume tends to decrease with increasing inherent moisture content for all of the samples, which can be attributed to hydrogen bonding between the coal macromolecules and water molecules. The relationship between the amount of adsorbed methane and the inherent moisture content can be characterized well using the linear and exponential models. And it can be found that the moisture effect coefficient is dependent on the coal rank. Further analysis indicates that the influence of inherent moisture on the methane adsorption capacity is more prominent for low rank coals, which is probably due to its greater hydrophilia and water-holding capacity. Whereas, the reduction in methane adsorption capacity is mainly controlled by the pore-blocking effect of adsorbed water for high rank coals, and the extent of the influence of inherent moisture is a little.

Effects of hydrothermal dewatering of lignite on rheology of coal water slurry

AbstractMaximizing the dry‐based solid loading of coal particles in water is essential in increasing the burning efficiency of coal water slurry, which has been widely used as a liquid fuel. Understanding the rheology of coal water slurry could provide fundamental guidance on designing and optimizing coal water slurry formulation. The rheological studies have shown that coal water slurries made with lignite samples after hydrothermal dewatering (HTD) exhibit a stronger shear thinning behaviour as compared with those made with raw lignite samples. The viscosity of coal water slurry at the shear rate of 100 s−1 decreases with an increasing HTD temperature, which is probably due to the decrease of volume of lignite particles caused by the permanent reduction of both bound and non‐freezable water (inherent moisture) after the HTD process. The reduction of the inherent moisture of lignite samples after HTD treatment was elucidated by differential scanning calorimetry (DSC) under the temperature well below the freezing point. A lignite water slurry with a solid loading of 62 wt% db (dry basis) is obtained after hydrothermal dewatering at 300 °C with the addition of 1.2 wt% of polycarboxylate ether (PCE). Our findings indicated that hydrothermal dewatering of lignite has profound impacts on the inherent moisture of lignite and the rheological properties of coal water slurry.

TENSILE PROPERTIES OF SURFACE TREATED COIR FIBRE REINFORCED POLYETHYLENE

The need to pursue an environmentally safer future has prompted the researchers to look beyond the inorganic fibre-based composites and engage in putting more thought into the utilization of natural fibre-based polymer composites. Although inorganic fibres, such as glass and carbon have a lot of advantages but we can owe its declining use in recent years to high initial cost, non-biodegradability, non-renewability, high energy consumption in manufacturing process and adverse environmental impacts. Natural fibres however more than compensate for their poor compatibility with the matrix, inherent high moisture absorption rate with their positive attributes like low cost, low density, non-abrasivity, good thermal properties, enhanced energy recovery and bio degradability. This work is aimed at investigating the effect of alkali treatment and fibre load on the tensile properties and hardness properties of coir fibre reinforced polypropylene composites. Polypropylene (PP) was used as the matrix resin and coir fibre (CF) as the reinforcing agent. The brown coconut fibres were pulled out and extracted manually from the coconut husks. To ensure proper interaction between fibre and matrix material, the outermost wax layer of the coir was removed by soaking the coir in hot water. The coir fibres are then prepared for treatment with NaOH solution to improve its surface properties and provide better adhesion with the matrix after the removal of lignin and pectin from the surface of the fibre. The tensile properties indicated that both the strength and modulus increased with increasing fibre content. However, in this investigation, the maximum fibre content is 20%. It could have been more than this but we encountered processing problem. Alkaline treated samples had higher tensile properties than untreated samples. The hardness of the material is not significantly affected by the surface treatment.

Influence of the microwave irradiation dewatering on the combustion characteristics of Chinese brown coals

This study investigates the influence of microwave irradiation on coal composition, pore structure, coal rank, and combustion characteristics of typical brown coals in China. Results show that the upgrading process significantly decreased the inherent moisture, and increased calorific value and fixed carbon content. After upgrading, pore distribution extended to micropore region, oxygen functional groups were reduced and destroyed, and the apparent aromaticity increased suggesting an improvement in the coal rank. Based on thermogravimetric analysis, the combustion processes of upgraded coals were delayed toward the high temperature region, and the temperatures of ignition, peak and burnout increased. Based on the average combustion rate and comprehensive combustion parameter, the upgraded coals performed better compared with raw brown coals and a high rank coal. In ignition and burnout segments, the activation energy increased but exhibited a decrease in the combustion stage.

Rethinking the Inherent Moisture Content of Biomass: Its Ability for Milling and Upgrading

The main obstacles to the widespread use of lignocellulosic biomass include its high moisture content and low grindability. Thus, we herein report a novel method, viz., the self-steam explosion (SE) method, which utilizes the moisture content of biomass to both reduce the particle size and enhance its properties. More specifically, the moisture content of the biomass sample is fully utilized as a steam resource to autohydrolyze the biomass component and yield fine particles with diameters <1 mm through self-explosion. This process differs from conventional steam explosion, which mainly employs saturated steam from external resources and requires wastewater treatment due to contamination of the steam, as the self-SE method offers flexibility in terms of the heating resources required in addition to a significant reduction in wastewater production. Furthermore, we demonstrated that this self-SE method effectively reduced the particle sizes of hardwood, softwood, and agricultural residues measuring 5–10 mm t...

Water-resistant hemp fiber-reinforced composites: In-situ surface protection by polyethylene film

The bottleneck in the broad use of natural fiber-reinforced composite (NFRC) is the poor water resistance due to the fiber inherent moisture absorption property. This study presented a unique technology that might revolutionarily solve this bottleneck of NFRC. A polyethylene (PE) film was adhered in-situ to the surfaces of the hemp fiber-reinforced composite by replacing the traditional vacuum bag during the vacuum assisted resin infusion (VARI) process. The water resistance and mechanical properties of composites were examined using contact angle tests, water absorption, mechanical property tests, dynamic mechanical analysis, and scanning electron microscope. Compared to the control NFRC samples, the contact angles of water, coffee and milk (three home pollutants) of PE film protected NFRC (PE-NFRC) dramatically increased from 46.1° to 82.5°, from 43.2° to 70.5°, and from 48.6° to 72.9°, respectively, and the 2h, 24h, and 120h water absorptions of PE-NFRC significantly decreased by 88.5%, 84.8%, and 68.5%, respectively. The results indicated that the water resistance of PE-NFRC was significantly improved. Based on comparisons of specific ultimate strengths of PE-NFRC and glass-fiber sheet molding compound (SMC), it is potential to replace glass fiber SMC by using PE-NFRC in the automotive industry.

Investigation into the ship motion induced moisture migration during seaborne coal transport

The inherent moisture in a coal cargo constantly migrates under the dynamic ship motion during maritime transport. The moisture often builds up at the bottom of the cargo. The accumulated water, if not removed sufficiently by the bilge well, can cause safety concerns during a voyage and difficulties during cargo unloading. The study presented in this paper aims to develop a program to investigate the moisture migration within coal cargoes in order to assess and eliminate shipping risks. The moisture migration phenomenon is initially modelled by adopting the classic infiltration theory, and considering the ship motions experienced by bulk carriers. An experimental method is developed to empirically characterise the moisture migration of a coal sample under simulated shipping dynamics. A predictive model is also developed to estimate the total moisture migration in a full size cargo by properly scaling up the experimental results. The model was validated by bilge well log collected from actual coal shipping voyages from Australia to international destinations.

Hydrocarbon gas generation by biochemical process of moderately barophilic methanogens in Barapukuria coal mine gas reservoir & aquifer

The research reported the biogenesis of hydrocarbon gases form the bituminous coal by moderately barophilic methanogens of coal mine water adjacent to underground aquifer and gas reservoir site of Barapukuria coal basin. Physiochemical characteristics of the coal (with zero gas baseline) as carbon source (Seam VI, 390m depth) for methanogens are determined. Parameters include inherent moisture content, volatile matter, ash content, calorific value, fixed carbon, α factor, H/C ratio, CHNSO elemental composition analysis, spectral assignments of ATR-FTIR, aromaticity factor fa and degree of aromatic ring condensation (R/C)u. Heavy, minors & light elements of calcined coal are also determined by X-ray fluorescence. Moderately barophilic methanogens surviving 5.61–6.45MPa lithostatic pressure (taking Barapukuria coal average specific gravity 1.43) are identified by fluorescence at ultraviolet region (100–400nm) of electromagnetic radiation and AQG-1 Methanometer. Bluish white fluorescence at UV is due to the redox coenzyme F350 in methanogens. Fluorescence at 350nm excitation is bluish white. The methanogens only have the ability to produce gas in presence of coal which acts as an electrode surface to take up electron for hydrogenase and other enzymes for formation of hydrocarbon gases. They also have the coal biodegradability. The methanogens yielded methane, ethylene, ethane, propane, iso-butane as detected by flame ionization detector of Bruker 450 gas chromatograph.

Utilization Biomass and Coal Mixture to Produce Alternative Solid Fuel for Reducing Emission of Green House Gas

This paper presents the characteristics of bio-briquette resulted from a series process using a mixture of raw materials. As raw materials of biobriquette production, this research used biomass corn cobs and banana peels, and a fine coal waste. Before using as component in the biobriquette, corn cobs, banana peels, and fine coal waste were carbonized. The carbonation process was carried out in temperature of 300-500 o C for 15 minutes. Carbonized corn cobs, banana peels, and a fine coal waste were characterized for calorific value and ash content. In this work, the influence of composition carbonized biomass and carbonized coal has been investigated. Before and after carbonization of biomass and coal, the calorific value and ash content of corn cobs were 4,239-6,386 kcal/kg and 3.47-8.12 % adb respectively, for banana peels were 4,135-6,042 kcal/kg and 16.99-32.31 % adb respectively, and for coal were 5,857-6,330 kcal/kg and 5.81-6.64 % adb respectively. The highest calorific value of biobriquette of 6,297 kcal/kg, highest fixed carbon content of 62.62 %, lowest volatile matter content of 26.18 % adb, lowest inherent moisture content of 5.14 % adb and lowest ash content of 6.06 were measured for composition of carbonized coal, carbonized corn cobs and carbonized banana peels ratio was of 1:4:0.

Experimental study on the effect of inherent moisture on hard coal adsorption–desorption characteristics

Coal is a complex geological body that is composed of organic material, gas, and water. Generally, coal with high hardness is commonly considered to be a non-outburst risk; however, several coal mines with hard coal seams in China have experienced coal and gas outbursts. Coals with different degrees of metamorphism have different inherent moisture ranges, which has a strong influence on gas adsorption and desorption. Currently, inhomogeneous moisture wetting remains an issue in traditional preparation methods for preparing coal samples with different moisture levels. In this paper, we chose three typical hard coals with different degrees of metamorphism and systematically studied their pore structure characteristics, effect of approximate inherent moisture on the gas adsorption–desorption characteristics, and gas diffusion of hard coals. The results show that all of the coal samples have an open pore structure, but each coal sample has different development characteristics of their pore structure. The higher the moisture, the shorter the adsorption equilibrium time required and the lower pressure drop. All of the adsorption isotherm curves fit the Langmuir equation well. The gas adsorption capacity of the same coal sample decreases gradually and the amplitude of the gas adsorption capacity decreases with increasing moisture. This relationship indicates that the existence of moisture occupies a certain space of the pore structure and reduces the gas adsorption sites of coal, reducing the adsorption and desorption amount of the coal samples. Moreover, low and middle rank coal can use the bidisperse model to calculate the diffusion coefficient, while high rank coal can use the unipore model. Increasing moisture causes the macropore diffusion coefficient D a,e and micropore diffusion coefficient D i,e of the YZG and YJ samples to decrease. The effective diffusion coefficient D e of the WLH samples also reduced gradually, which suggests that moisture has an influence on the gas migration and diffusion channels of coal, reducing the gas adsorption equilibrium time, desorption rate, and diffusion rate of coal seam.

Evolved gas analysis of PEP-SET sand by TG and FTIR

Thermogravimetric analysis coupled with Fourier transform infrared spectroscopy (TG-FTIR) and on-line FTIR were employed in this study, aiming at investigating the pyrolysis characteristic of Polybenzylic Ether Phenolic resin sand mould (PEP-SET sand) and emission gases generated during casting. The non-isothermal pyrolysis of PEP-SET sand can be subdivided into three stages: emission of inherent moisture (below 215°C), thermal decomposition at low temperature (215–315°C) and further cracking process at high temperature (315–432°C). The main emission gaseous products in pyrolysis processes were H2O, CO2, NH3, CH4, C2H6, NO and a little amount of CO, according to the FTIR spectrum analyses. The amount of N-containing pyrolysis products generated from cracking of the CN bond reflects the collapse extent of the binder. The thermal shock tests at different temperatures were performed. Similar to non-isothermal pyrolysis processes, the main gaseous products were CO2, CO, NO, CH4 and C2H6 under thermal shock conditions, and these gases released follow a fixed sequence: concentrations of CO, CO2 and NO firstly increased to the peaks and then decreased with the rising of CH4 and C2H6. At last the CO2 concentration increased again. The major emission oxidizing gas which may induce ignition of Mg melt is CO2 and the environmental hazardous components are NO and NH3.

Hydrogen-rich gas production from pyrolysis of wet sludge in situ steam agent

A series of wet sludge samples with different moisture contents were pyrolyzed in situ steam in a bench-scale fixed bed reactor in order to examine the influence of moisture and temperature on product distribution and gas composition. The results demonstrated that inherent moisture in wet sludge had a great effect on the product yield. The pyrolysis of wet sludge (43.38% moisture content) at 800 °C exhibited maximum H2 yield (7.76 mol kg−1 dry basis wet sludge) and dry gas yield (0.61 Nm3 kg−1) and H2 content of 42.13 vol%. When the moisture exceeded 43.38%, H2 yield and gas yield both tended to decline. It was also shown that the elevated temperature exhibited a significant influence on gas content increase and tar reduction; at the same time, H2 yield and H2 content were increased from 1.83 mol kg−1 dry basis wet sludge and 16.67 vol% to 9.15 mol kg−1 dry basis wet sludge and 45.67 vol%, respectively, as temperature increased from 600 °C to 850 °C. LHV of fuel gas varies from 15.49 MJ Nm−3 to 11.65 MJ Nm−3 because of decrease in CH4 and C2H4 content as temperature increasing. In conclusion, hydrogen rich gas production by pyrolysis of wet sludge which avoided pre-drying process and utilized in situ steam agent from wet sludge is an economic method.

Ultra-High Purity Hydrazine Delivery for Low Temperature Metal Nitride ALD

Introduction Next generation channel materials (SiGe, Ge and InGaAs) place very difficult thermal constraints (<400C) on Metal Nitride deposition methods. New low temperature methods are potentially needed for: SiN passivation layers on new channel materialsSiN sidewall spacers and contact etch stop layersTiN for metal gate electrodesTiN or WN barrier layers for W contactsTaN barrier layers for Cu Early studies have shown the potential viability of hydrazine and its derivatives as a low temperature Nitrogen source in thermal ALD.1-3 Challenges Though theoretically appealing, an early problem encountered in this approach was the lack of vaporization sources for pure anhydrous H2NNH2gas. There are several challenges associated with the use of anhydrous hydrazine, as it is known to be highly flammable and toxic. In addition, current commercial sources lack the purity needed for semiconductor manufacturing. Membrane Technology Our approach toward increasing safety entails the use of a membrane delivery system where hydrazine is dissolved in an organic solvent (Figure 1). Hydrazine gas permeates the membrane and is delivered to the process chamber, while the solvent does not permeate and remains in the liquid state. Hydrazine vapor pressure is maintained at levels viable for current atomic layer deposition process requirements. The addition of a high boiling point solvent raises the solution flash point, reducing explosive risk. Low Temperature Deposition Initial implementation of our novel hydrazine vaporizer focused on the passivation of SiGe(110) surfaces. Atomic layer deposition of a silicon rich SiNx control layer on Si0.7Ge0.3(001), Si0.5Ge0.5(001), and Si0.5Ge0.5(110) surfaces has been achieved by sequential pulsing of Si2Cl6 and N2H4 precursors at a substrate temperature of 285°C. XPS spectra show a higher binding energy shoulder peak on Si2p indicative of SiOxNyClz bonding while Ge2p and Ge3d peaks show only a small amount of higher binding energy components consistent with only interfacial bonds and indicating the growth of SiOxNy on the SiGe surface with negligible subsurface reactions. Scanning tunneling spectroscopy (STS) measurements confirm the SiNx interfacial control layer forms a passivating interfacial layer on both p-type Si.70Ge.30(001), Si.50Ge.50(110), and Si.50Ge.50(001) surfaces as the surface Fermi level was unpinned and the electronic structure was free of states in the band gap. Significant amounts of oxygen are incorporated into the SiNx layer due to handling procedures as well as the inherent moisture levels in the starting liquid hydrazine material. However in this instance, SiOxNy layer serves to improve the SixGe1-xsurface by preventing formation of Ge-O bonds, therefore it is not a detriment as would be expected in other applications. Hydrazine Measurement and Purification Measurement of water levels inherent to liquid hydrazine has been established to a LDL of 10 parts-per-million using Karl-Fischer and GC-MS methods. Gas phase moisture measurements have been carried out to an LDL of 800 parts-per-billion. Water content in gas phase hydrazine has now reached less than 1.0ppm, which is comparable to Semiconductor grade ammonia. Conclusion There is an emerging need for sub-400C metal nitride deposition. We have developed a novel hydrazine vaporization source and demonstrated that hydrazine is a viable precursor to enable low temperature ALD. Lack of liquid source purity initially posed a problem for films such as TiNx. Our new results indicate that we have overcome the purity issue by reaching hydrazine purity levels comparable to semiconductor grade ammonia. Ultra-high purity hydrazine is now being used for sub 400C deposition of high quality TiNx. XPS, AFM and sheet resistance of this material will be presented. References S. Wolf, M. Edmonds, T. Kent, D. Alvarez, R. Droopad and A. C. Kummel, AVS 2015, San Jose, CA, Paper EM+NS+PS-MoA7, (2015).K. Bernal-Ramos, T. Chen, R. Kanjolia, Y. J. Chabal, “The Role of Hydrazine and its Derivatives in Atomic Layer Deposition of Tungsten Nitride Thin Films”, presented at AVS ALD, Kyoto, Japan, June 2014.B. B. Burton, S. W. Kang, S. W. Rhee and S. M. George, J. Electrochem. Soc., 155(7), D508-D516, (2008). Figure 1

Influence of Inherent Moisture on the Formation of Particulate Matter during Low-Rank Coal Combustion

Influence of Inherent Moisture on the Formation of Particulate Matter during Low-Rank Coal Combustion

Highly enhanced long time stability of perovskite solar cells by involving a hydrophobic hole modification layer

Recently, much progress has been achieved in the lab prototype perovskite solar cells (PSCs), however, the challenging toward the commercial production of PSCs still remains, which is their low stability due to the inherent moisture sensitivity of the perovskite photoactive layer. In this work, a hydrophobic hole modification layer, zinc phthalocyanine (ZnPc), is introduced to the typical planer hetero-junction (PHJ) structure to improve the device performance and prevent moisture. The ZnPc based devices show an improved power conversion efficiency (PCE) of 16.8% compared to 15.1% for the unmodified devices, and highly enhanced long-term stability (91% of initial PCE remains after 2400h), which is the best report for PSCs in ambient environment without sealing. In addition, pulsed laser deposition (PLD) technique is used to prepare electron collection layer Nb-doped TiOx in PSC fabrication process. Devices with large area (225mm2) and flexibility were also fabricated in this study to demonstrate the potential practical application of this strategy. This work paves a way for the developments of PSCs with long-term stability and demonstrates a strategy toward practical applications for PSCs.

Suppression of Water Absorption by Molecular Design of Ionic Liquid Electrolyte for Li–Air Battery

In this study, the effect of water on the oxygen reduction reaction is initially investigated in aprotic ionic liquids by cyclic voltammetry, revealing that the presence of water significantly deteriorates the reversibility of the oxygen reduction reaction and oxygen evolution reaction, which will be detrimental to performance of a practical lithium–air battery. In order to prevent moisture intrusion from ambient air, a hydrophobic electrolyte is then designed and the moisture content in the electrolyte exposed to ambient air is greatly suppressed, to less than 1 wt% at 30 °C and 90% RH (relative humidity). Charge and discharge tests using the hydrophobic electrolyte are reversible for several cycles even in O2 with a RH of 28%. This approach for enhancing the hydrophobicity of the electrolyte, and thus the inherent equilibrium moisture content, for the Li–air battery demonstrates the possibility for improved stability to ambient moisture.

Integration of pyrolysis and entrained-bed gasification for the production of chemicals from Victorian brown coal — Process simulation and exergy analysis

This paper introduces a novel process for the integration of pyrolysis and entrained-flow gasification for the as-mined Victorian brown coal containing 65wt.% moisture. An initial mild pyrolysis of coal is proposed to reduce moisture content, and produce multiple products including char, tar and hydrogen-rich coal gas. Subsequently, the resulting water-free char is subjected to an entrained-flow gasifier, upon the blending of silica additive or high-ash bituminous coal. The resultant syngas passes through a cleaning unit and water gas shift reactor before mixing with the pyrolysis-derived gas to reach a target H2/CO molar ratio of 2.0 that is essential for the synthesis of a number of chemicals. In this paper, process simulation and exergy analysis were conducted to prove the advantages of the proposed process against the conventional drying–gasification combination. The results show that, the proposed pyrolysis–gasification integration process for Victorian brown coal possesses an exergy efficiency 4.5% higher than the drying–gasification process, and 1.5% higher than the drying case for another lignite containing 25wt.% moisture. A prior removal of 20% of the inherent moisture can further improve the exergy efficiency by 4% for Victorian brown coal. The addition of 20% of black coal is the optimum ratio to improve the ash slagging propensity, as well as improve exergy efficiency compared to the conventional drying–gasification process.

Formation of Methane Clathrate Hydrates in Coal Moisture: Implications for Coalbed Methane Resources and Reservoir Pressures

Adsorption, X-ray diffraction, and nuclear magnetic resonance analysis of subbituminous to high-volatile bituminous coal at in situ moisture content, low temperatures, and moderate pressures demonstrate that a significant proportion of the inherent moisture (nonmobile water) is available to form methane clathrate hydrates. These results have implications for coal gas resources and reservoir pressures in current areas of permafrost and the much larger regions that were glaciated during the Pleistocene. Methane adsorption tests indicate the clathrates form comparatively rapidly in coal micro- and mesopores from an immobile water phase, at lower pressures than those formed in macroporous materials. At successively higher experimental pressures, hydrates nucleate and grow rapidly on the scale of minutes to hours, until an “apparent” equilibrium pressure is reached. The onset of hydrate formation at 0 °C is at about 3.25 MPa for a Tarn coal with 33% moisture and at slightly higher pressures for the other coals with lower inherent moisture. The amount of gas consumed in hydrate formation, in excess of that attributed to sorption, is 11.6 cm3/g coal for the Tarn coal (Alaska) with 33% moisture, 8.15 cm3/g coal for a Dietz coal (Wyoming) with 22% moisture, and 1.85 cm3/g coal for a Texas coal with about 8% moisture. On a volume of gas (STP) per volume of water basis at 8 MPa, the Tarn and Dietz coal have similar values (35 and 37 cm3/cm3), whereas the Texas coal is measureably less (24 cm3/cm3). At 8 MPa and 0 °C, about 20% of the inherent moisture has participated in hydrate formation for the Tarn and Deitz coals and 13% for the Texas coal. If hydrate formation strips methane from the sorbed state, the proportion of water contributing to hydrate calculates was over 100% for the Texas coal, which suggests that methane is mainly forming from free gas. The methane hydrates analyzed by X-ray diffraction and nuclear magnetic resonance (NMR) spectroscopy are cubic (Pm3n̅ space group) and have small and large cage sI structures. NMR and PXRD spectra indicates that the small cages are about 90% occupied, while the large cages are completely full, yielding a stoichiometry of ca. CH4·6H2O, which is consistent with other natural hydrates. There is some evidence that some methane gas remains trapped in the smallest pores, whereas the hydrates occupy large pores, which may be due to the suppression of hydrate formation by high capillary pressures. The formation of methane hydrates, particularly in low-rank coals, markedly increases the capacity of the coal to store gas. Depending on the coal moisture content and coal rank, methane storage capacity in gas hydrates is up to 2 orders of magnitude greater than the gas storage capacity of the coal by sorption alone. Since low-rank coals invariably have high moisture content, if the strata lie with the hydrate stability zone, significant gas storage in hydrates is anticipated, if gas is available. At the low temperature required for hydrate formation, however, self-sourced methane from methanogenesis or thermal alteration is not anticipated. Successive formation and dissociation of methane hydrates during glacial and interglacial times in the Pleistocene can be anticipated to have impacted shallow gas reservoirs, including coals, to depth up to about 800 m, depending on the surface temperature and geothermal gradient. It is speculated that during the Pleistocene free and sorbed coal gas was scavenged during the formation of hydrates, and this process may explain the low gas content of some high-latitude coals. Similarly, lower than anticipated pore pressure and lack of free water in the Horseshoe Canyon coals in western Canada may be the result of dissociation of hydrates forming overpressures, which potentially could hydraulically fracture the coal and flush the coal of free water. Subsequent dissipation of the gas pressure would lead to the current low reservoir pressure.

Mapping of coal quality using stochastic simulation and isometric logratio transformation with an application to a Texas lignite

Coal is a chemically complex commodity that often contains most of the natural elements in the periodic table. Coal constituents are conventionally grouped into four components (proximate analysis): fixed carbon, ash, inherent moisture, and volatile matter. These four parts, customarily measured as weight losses and expressed as percentages, share all properties and statistical challenges of compositional data. Consequently, adequate modeling should be done in terms of a logratio transformation, a requirement that is commonly overlooked by modelers. The transformation of choice is the isometric logratio transformation because of its geometrical and statistical advantages. The modeling is done through a series of realizations prepared by applying sequential simulation for the purpose of displaying the parts in maps incorporating uncertainty. The approach makes realistic assumptions and the results honor the data and basic considerations, such as percentages between 0 and 100, all four parts adding to 100% at any location in the study area, and a style of spatial fluctuation in the realizations equal to that of the data. The realizations are used to prepare different results, including probability distributions across a deposit, E-type maps displaying average properties, and probability maps summarizing joint fluctuations of several parts. Application of these maps to a lignite bed clearly delineates the deposit boundary, reveals a channel cutting across, and shows that the most favorable coal quality is to the north and deteriorates toward the southeast.

Sulfur Transformation during Hydrothermal Dewatering of Low Rank Coal

The presence of sulfur in coals has raised serious environmental issues, which are obstacles to large-scale utilization of coals. Hydrothermal dewatering (HTD) is a promising upgrading method for low-rank coals (LRCs) to significantly remove oxygen-containing groups and irreversibly decrease the inherent moisture content. To uncouple the complex behavior of sulfur evolution during HTD processing of lignite and to elucidate the main mechanism, this research experimentally studied the characteristics of sulfur transformation in a Chinese lignite from Xiaolongtan coal mine during HTD upgrading. Results reveal that the HTD upgrading of raw coal within the temperature range from 200 to 300 °C can obtain a desirably upgraded coal with higher calorific value and lower inherent moisture. Compared with raw coal, organic sulfur content decreased significantly, whereas sulfate sulfur content gradually increased after HTD. X-ray photoelectron spectroscopy results showed that HTD promoted aliphatic sulfur decompositio...