Surface Of Coal Particles Research Articles

Biogenic methane potential for Surat Basin, Queensland coal seams

Produced water samples collected from Surat Basin coal seams in eastern Queensland, Australia were shown to contain viable microbial consortia with the ability to convert native Walloon coal into methane. Methane generation rates of up to 1.0 m3/t coal/day (30 scf/ton/day) were observed, with overall yields up to 6.5 m3/t coal (210 scf/ton); in comparison, total methane reserves for the Surat Basin are typically 4 to 8 m3/t. This is the first direct evidence of real-time biogenic coal-to-methane potential for an Australian coal seam sample. Six of the eight Surat Basin water samples tested positive for biomethane production when H2–CO2 was provided as the sole methanogenic substrate; five produced methane from methanol, but acetoclastic methanogenesis was not observed. An active H2–CO2 pathway could have implications for the conversion of sequestered CO2, if an in-situ source of reduced hydrogen is present in excess. In a simple experiment, biomethane production from a Walloon coal was not enhanced when the bicarbonate concentration in the medium was doubled. It is anticipated that the low surface area/solubility of coals may limit their bioavailability; coal-to-methane rates and final yields increased in proportion to the coal particle surface area. Similarly, when a Zonyl FSN surfactant was added to improve coal bioavailability, the initial methane production rate increased by 240%, and the final methane yield increased by 180% in comparison to a no-surfactant control. Overall, these results suggest an opportunity to enhance Surat Basin coalbed methane reserves via in-situ stimulation of indigenous microbial consortia.

Leaching characteristics of bromine in coal

Comparative column leaching experiments were carried out on coal samples collected from Moxinpo Mine in Chongqing, Southwest China. Different acid solutions were used to investigate the leaching behavior and potential environmental effects of bromine in coal. The leaching rate and maximum leached concentration of bromine were calculated on the basis of the concentration of bromine in different resulting leachates measured by inductively coupled plasma mass spectrometry. The results show that the modes of occurrence and locations of bromine in coal, time, and pH value play an important role in controlling the leaching behavior of bromine in coal. At 120 h, the maximum leached concentration and the total leaching rate of bromine in coal increased with an increase in the acidity of the leaching solution. The amount of bromine released from coal leached at a pH of 2 accounted for 80.65% of its total leached amount for 40 h, whereas it was 89.42% at a pH of 4 for 50 h. When leached by an acidic solution, the bromine present in carbonate and Fe–Mn oxides located on the surface of coal particles may be released first, followed by the bromine in water-soluble and exchangeable forms in the interior of the coal matrix. The experiment showed that the bromine in coal may be leached out by acidic rain and enters the surrounding soil and surface water, resulting in the enrichment of bromine in the environment.

Morphological characterization of super fine pulverized coal particle. Part 2. AFM investigation of single coal particle

Super fine pulverized coal combustion is a new pulverized coal combustion technology which has better stability, higher combustion efficiency and lower NO x and SO 2 emission than that using conventional particle sizes. In this paper we applied fractal analysis based on power spectral density (PSD) and slit island method (SIM), three-dimensional (3D) surface roughness measurement and surface-topography observations from AFM to form a proper investigative tool which may give a relatively full picture of surface morphology of super fine pulverized coal particles for the first time. The final results indicate that both fractal dimensions calculated by SIM and PSD and roughness of coal particle size increase with the increase of the coal particle size. Besides, the grey relational analysis was used to study the degree of relative importance of the influential factors about the microroughness of coal particle surfaces. The results show that the influence of the coal particle size is the greatest compared with the coal qualities and fractal dimensions. This work provides some reference for a relatively full picture of surface morphology of super fine pulverized coal particles. The findings from this work will be helpful to form the basis and provide guidance for further studies on the chemical and combustion characteristics of super fine pulverized coal particles.

Nanobubble generation and its applications in froth flotation (part II): fundamental study and theoretical analysis

Froth flotation is a commonly employed technology to improve the quality of raw coal and minerals. Coal and minerals particle size and surface hydrophobicity are two main parameters that affect three key steps in froth flotation process: particle-bubble collision, adhesion, and detachment. This paper fundamentally investigated the effects of nanobubble on coal and phosphate flotation. It has been found that the presence of nanobubble in flotation pulp could widen the coal and phosphate flotation particle size range, increase the particle surface hydrophobicity, and thus improve the coal and phosphate froth flotation recovery.

Characterization of a methanogenic consortium enriched from a coalbed methane well in the Powder River Basin, U.S.A.

Abstract Well-bore water samples from the Fort Union Formation in the Powder River Basin of Wyoming tested positive for the presence of living microbial communities capable of generating methane from Wyodak coal under laboratory conditions. The methanogens in this consortium produced methane from acetate and methanol, but did not produce methane from a H2–CO2 headspace. This was consistent with a phylogenetic analysis of archaeal 16S ribosomal deoxyribonucleic acid (rDNA) sequences from the enrichment culture, which revealed just two phylotypes, both closely related to Methanosarcina mazei. Phylogenetic analysis of bacterial 16S ribosomal ribonucleic acid (rRNA) genes revealed phylotypes similar to the acetogens Acidaminobacter hydrogenoformans and Syntrophomonas sp., and to known fermentative species. This methane-producing consortium was maintained on a defined microbial medium supplemented with Wyodak coal plus 50 mg/L yeast extract as the sole carbon substrates. At 22 °C, the maximum methane production rate was 0.084 m3/t coal/day (2.7 scf/ton/day); in comparison, total methane reserves in the Powder River Basin are approximately 1.6 to 2.2 m3/t (50 to 70 scf/ton). When the incubation temperature was increased from 22 °C to 38 °C, the rate of methane production increased by 300%; similarly, when the culture medium pH was lowered from 7.4 to 6.4, the methanogenesis rate increased by 680%. Increasing the coal particle surface area by 890% via smaller particle size increased methane production rates by over 200%. Microbial methane production in coal slurries was also enhanced by the addition of the solvent N,N-dimethylformamide (DMF). These results suggest an opportunity to enhance coalbed methane reserves by stimulating the activity of existing methanogenic consortia in-situ; in particular, reservoir treatments that enhance coal solubility and dissolution rates may be beneficial.

An Experimental Study of Temperature of Burning Coal Particle in Fluidized Bed

The purpose of this study was to investigate the temperature of coal particle during combustion in fluidized bed (FB). It is necessary to know the coal particle temperature in order to predict kinetics of chemical reactions within and at the surface of coal particle, accurate NOx and SO2 emission, fragmentation, attrition, the possibility of ash melting, etc. The experimental investigations were conducted in order to obtain the reliable data on the temperature of particle burning in the FB. A method using thermocouple was developed and applied for measurements. Thermocouple was inserted in the center of the particle shaped into spherical form with various diameters: 5, 7, 8, and 10 mm. Two characteristic types of low-rank Serbian coals were investigated. Experiments were done at the FB temperature in the range of 590−710 °C. Two types of experiments were performed: (i) combustion using air as fluidization gas and (ii) devolatilization with N2 followed by combustion of obtained char in air. The temperatu...

石炭灰堆積層中の水分凝縮による固化現象の数値解析

In this study, hardening phenomena of coal ash beds in high-humidity condition are examined. We employ a diffusion simulation in clarifying the distribution of condensed water in coal ash beds, in which water vapor is absorbed into sulfur trioxide adhered on the surface of coal ash particles. Aqueous sulfuric acids solution formed by the absorption is in equilibrium with the ambient water vapor. The diffusion rate of water vapor is proportional to the difference between the pressure and ambient water vapor pressure. The simulation successfully describes the results of previous experiment, at a constant temperature, with the variations in the equilibrium moisture and particle diameter of coal ash. Moreover, it is clarified that the relationship between water content and hardening phenomena is very similar for various coal ashes, with a correction of particle diameter of coal ash and the volume of condensate bridging between particles.

Effect of Mechanically Activated Sorption on the Rheological Behavior of Coal Slurries

It is shown that the mechanically activated sorption of surfactants on the surface of coal particles substantially affects the rheological properties of highly concentrated coal–water slurries: their viscosity may be decreased several times.

Adsorption of a non-ionic dispersant on lignite particle surfaces

The concentration and viscosity of the slurry are related to each other, and they have a unique importance in the case of industrial application of the slurry. It is well known that the fluidity of a coal–water slurry with a high coal concentration is largely affected by the nature of the dispersing agent. Therefore, there are good reasons for seeking an understanding of the adsorption behavior of the dispersants on the coal particle surfaces. The aim of this investigation is to determine the adsorption behavior of a non-ionic dispersant, polyoxyethlene sorbitan monooleate, on Turkish lignite samples. The effects of the dispersant concentration, temperature, time and pH on dispersant adsorption were investigated systematically. The results are also analyzed by a two level factorial design matrix to explain the effects of the parameters on the adsorption, and multilinear mathematical models representing the adsorption behavior of the dispersant used within the experimental conditions are proposed for each coal sample used.

97/03959 Modeling the application of Kalina cycle to LEBS power plants

The utilization of oily sludge produced from refinery processes was evaluated in this study. Oily sludge was added to coal–water slurry (CWS) in different ways to prepare desirable coal–oily-sludge slurry (COSS). The slurryability and rheological characteristics of COSS were investigated and compared to CWS. The viscosity and yield stress of COSS sharply decrease with increasing the addition of oily sludge that preferentially wets coal particles. Microscopic structure and surface functional groups examination proved that oil droplets present in oily sludge could form a thin hydrophobic membrane on coal particle surface and modify its surface properties. The maximum solids loading can be either increased or decreased depending on the slurry preparation method. The maximum solids loading of COSS increases from 62.2 wt% to 64.0 wt% when oily sludge that preferentially wets coal was added in a ratio of 10.0 wt%.

96/04606 Fractal approach to coal particle surface

A number of concentrates of vitrinite, liptinite and inertinite groups of macerals, prepared and sealed under nitrogen by Fenton and Smith, have been made available to us. They are being studied in a number of institutions using various techniques. The set comprises seven vitrinites, four liptinites and eight inertinites, the last-named including some reputed semifusinite concentrates. Identifications of seams and sample history are provided here, together with chemical analyses and re-analysis of petrographic compositions using reflected light methods. The vitrinites cover a range of rank represented by carbon contents from 81.5 to 91.4% dmmf (hvB to Iv). The liptinites consist very largely of sporinite. Dilatation tests indicate that little if any weathering has occurred during 20 years of storage of the vitrinites.

Significant factors affecting devolatilization of fragmenting, non-swelling coals in fluidized bed combustion

A theoretical study has been made to identify those variables having a statistically significant effect on the devolatilization of fragmenting coals. To achieve this objective, a simple mathematical model has been developed for prediction of the devolatilization time of fragmenting coals and the number of fragmentations during devolatilization in conditions relevant to fluidized bed combustion. It incorporates important phenomena occurring during coal devolatilization, namely heat transfer from the bed to the surface of the coal particle, heat transfer inside the devolatilizing coal particle, primary decomposition reactions, transport of released volatiles from the coal matrix to the surface of the coal particle, and devolatilization-induced fragmentation. The model has been used for a factorial evaluation to determine significant variables affecting the devolatilization of fragmenting coals. Eight factors and two responses were selected, the responses were devolatilization time and number of fragmentations. Results of the factorial evaluation show that for both responses, the devolatilization of 1–20 mm diameter coal particles at 1023–1223 K is predominantly governed by coal particle diameter. The devolatilization time is also significantly affected by coal thermal properties, and less significantly by bed temperature and reaction rate of devolatilization. In addition to coal particle diameter, the number of fragmentations is significantly affected by variables related to volatiles transport to the coal particle surface, i.e. the diameter of coal convective pores and the viscosity of volatiles.

Coal particle surface characteristics and the surface smoothness factor in theory of combustion

Coal particle surface characteristics and the surface smoothness factor in theory of combustion

Studies on Coal Slurry Fuel(Part 4). Effects of Additive and Particle Size Distribution on Characteristics of Coal-Water Mixture(CWM).

Six anionic polyelectrolytes (poly(styrenesulfonate) (PSS), three poly(isoprenesulfonate)s (PIPSs), a copolymer of sodium poly(methacrylate) and poly(methacrylate) ester (PMA), and a melamineformaldehyde condensate sulfonate (MFCS)) were tested for additives for coal-water mixtures (CWMs), which were, prepared either by dry grinding method or by wet grinding method, and evaluated by their viscosity and storage stability. A poly(isoprenesulfonate) PIPS-1 was found as effective as PSS, which is now most commonly used in practical CWM processes. A new parameter is proposed. The parameter is defined as the minimum quantity of liquid (water: ethylene glycol 4:6) necessary for a certain amount of powdery coal to form a putty-like lump when the liquid is titrated on the powdery coal. Liquid-absorption reveals the quantity of the liquid that is tightly retained on the surface of coal particles and locked in the apertures of the particles. Various powdery coals, for which their mean particle sizes were adjusted to be about the same while their size distributions remained different, were prepared. For CWMs prepared from powdery coals, when the size of coal particles was more distributed, the liquid-absorption was reduced and the CWM viscosity was decreased. By use of powdery calcium carbonates, it was found that liquid-absorption for the powders was influenced both by the magnitude of the apertures of the particles and by the specific surface area.

Factors Influencing the Moisture Content of Coarse Coal After Centrifugation

High moisture contents in export coals increase transport and handling costs and can result in contract penalties. Considerable efforts have been focussed on fine coal dewatering, but the significant variations in the moisture content of the coarse product are also important. Very little work has been carried out to determine the magnitude and causes of these variations. An AMIRA funded project has been conducted to investigate this problem. An on-line moisture monitor was installed on the product belt immediately after the first coarse coal centrifuge at two coal preparation plants to continuously measure the moisture content of the coal from a single centrifuge. Samples were taken over a range of operating conditions and at times of low and high product moisture contents. The coal samples were characterised by a range of techniques and those properties correlating with moisture content variations have been identified. Basic studies were also conducted with a laboratory centrifuge specifically designed to characterise various coarse coal samples in terms of their water retention capacity. It has been established for the plants investigated, that the moisture of the coarse coal (typically 6 to 9%) can vary by at least one percent at a particular plant, and a number of percentage points between plants. An empirical model has been developed which can explain about 80% of the variation of the moisture content of the coarse coal from the 25 samples investigated. The rank of the coals ranged from 0.7 to 1.65 mean reflectance. The model identified four principle controlling factors: (i) The amount of moisture held internally within the coal, as measured by the new laboratory centrifuge technique. (ii) The specific surface area of the coal being presented to the centrifuge. (iii) The rank of the coal as measured by reflectance. (iv) The amount of ultra-fine (slimes) material associated with the coarse coal, which can affect the drainage of water from the coal particle surface. The hydrophobicity (rank) of the coal and the ultra-fine particles hinder the water flow from the coarse particles. This model provides an estimate of the moisture level which can be achieved by centrifugation of coarse coal.

The removal of residuum from low rank coal particles after use of hot residuum to eliminate moisture

One recently considered concept of beneficiation of low rank coal is elimination of moisture by immersion of the coal in hot heavy oil. The problem of the subsequent drainage of oil from the coal particles is cited as a major difficulty of this process. In the present paper a theoretical analysis of drainage hydrodynamics has been carried out to indicate the practical possibility for application of combined centrifugal, aerodynamic and gravitational forces to drain effectively excess oil from the surface of coal particles. Experiments on aerodynamic and gravitational drainage have confirmed the appearance of acceptable efficiency of drainage predicted by theoretical calculations.

MICROBIALLY FORMED CATALYSTS FOR ENHANCEMENT OF DIRECT COAL LIQUEFACTION

Abstract The present study examines the potential to biologically precipitate active catalytic compounds on the surface of coal particles in a water slurry. These compounds could be active forms of iron, an element abundant in coal, or active forms of molybdenum added as a soluble salt. The acidophilic microorganisms Thiobacillus ferrooxida/ns and Acidianus brierlyi were added to a 5% coal slurry at a pH of 3·0 or less. Experiments were carried out for 21 days in shake flasks/automated fermentor at constant temperature and pH. Deposition of iron and molybdenum compounds on the particle surface was confirmed by several spectroscopic methods. After bio-treatment, the coal was removed by filtration and dried. A sample was then liquified in a bomb at 385°C in tetralin and hydrogen for 15 minutes. In some runs the sulfiding agent dimethyl disulfide (DMDS) was added to the mixture. Separation of the products was by soxhlet extraction. Total conversion, gas + oil + asphaltenes + preasphaltenes, of the pretreated...

Influence of pitch coal surface treatment on the beneficiation of high water content coal and the rheological properties of CWS

The influence of pitch coal surface treatment on the beneficiation of high water content coal and preparation of its highly concentrated coal-water slurry (CWS) has been investigated. Weak slurryability coal, containing a high water content, exhibited a high degree of hydrophilicity. Having been treated by pitch during milling, the surface of coal particles became increasingly hydrophobia Coal powders treated and untreated with pitch were beneficiated in the oil-water system for comparison. The value of ash reduction of the pitch treated coal powders was higher than that of the untreated ones after beneficiation. The untreated, treated and beneficiated coals were used to prepare highly concentrated CWS by adding additives. The results of rheological experiments show that the CWS of beneficiated coal after treatment with pitch had lower viscosities compared with the CWS of the untreated coal or treated coal without beneficiation.

The effects of solids and reagents on the characteristics of coal flotation in columns

The effect of solids and chemical addition on column flotation of coal was investigated by examining the changes in the flow characterization and flotation performance. It was found that larger feed particles reduce the stability and the thickness of froth zone. While the addition of collectors (kerosene) increases the coal particle surface hydrophobicity, thus accelerating the froth collapse, bubble coalescence, and reducing the gas holdup; adding a frother increases the ratio of recovery of coarse particles (+200 μm) to that of fines. Using Dowfroth 250 as frother resulted in higher recovery and flotation rate constants, as well as the recovery of larger particles than in the case of MIBC. A method for predicting the bubble loading in flotation columns is proposed.

Effect of preparation techniques on kinetics of oil agglomeration of fine coal

The present study was carried out to establish whether the air adsorbed on fresh coal particle surfaces created by dry grinding affects the subsequent agglomeration of an aqueous suspension of the particles with oil. The agglomeration response of coal suspensions which had been degassed by applying a moderate vacuum were compared to those which had not been degassed. Aqueous suspensions of No. 2 Gas Seam coal from Raleigh County, West Virginia, were agglomerated with hexadecane in a closed mixing system. A photometric dispersion analyzer was used to monitor the turbidity of a suspension undergoing agglomeration. The behavior of both wet- and dry-ground samples was established in a series of runs made with oil dosages ranging from 1 to 33 v/w%. The presence of an air film on highly hydrophobic coal particles appeared t increase both the initial rate and final extent of agglomeration by making it easier for the oil to wet the coal particle surface and by reducing the amount of oil required to bond the agglomerates. The effects were particularly pronounced when low oil dosages were used. The presence of an air film was significant only for dry-ground coal. Since different results were achieved with wet-ground coal and dry-ground coal which had been degassed, it does not seem possible to simulate wet grinding by degassing dry-ground coal prior to agglomeration.