Coal Fragments Research Articles

Stationary combustion: The environmental leitmotiv

Combustion and pollutant formation are inseparable processes. Because of the central role of direct fossil fuel utilization in the provision of heat and power for the foreseeable future, major efforts are being made to ameliorate the environmental effects. The most cost-effective way of reducing pollutant emission is the modification of the combustion process. Combustion scientists and engineers have developed new clean combustion technologies based on the better understanding of the physicalchemical bases of NOx formation and destruction in flames, the capture of SO2 by additive sorbent or ion-exchangeable alkali compounds, the formation and destruction of PACs, and the formation of fine inorganic aerosols in high temperature combustion processes. New information has become available on the mechanism of coal combustion, on the effect of fragmentation of coal and char particles upon the rates of heterogeneous reactions of carbonaceous solids and on the development of the fly ash size distribution. It is of interest to note that while it is combustion chemistry that provides guidance for the development of combustion processes with reduced pollution emission, the realization of the required concentration-temperature history of the fuel in furnaces, boilers and combustors represents a challenge to combustion physics, notably fluid dynamics and heat transfer.

Formation and behavior of submicron fly ash in pulverized coal combustion furnace

In this study, the formation mechanism and the behavior of submicron fly ash (SFA) (larger than 0.1 μm) in the industrial type pulverized-coal combustion furnace was examined experimentally by using two different models of furnace: a turbulent furnace, which was designed to realize practical combustion conditions, and a small, laminar flow furnace. Observations were made by an electron micrograph, x-ray microanalysis, and infrared spectroscopic analysis of the submicron particles sampled from the furnace, and measurements of the concentration distribution of the suspended and coagulated SFA were carried out. Both the electron micrographs and the infrared spectroscopic analysis showed that the submicron particles sampled near the concentration peak in the furnace closely resembled raw coal. The major components (aluminum, silicon, calcium, and iron) in the ash contained in the submicron raw coal fragment was compared with the SFA sampled at the flue for six different coals. The composition of the SFA was mostly compared to that of the raw coal fragment. There was no silicon condensation in these coals, with one exception. The measured concentration distribution of the SFA in the furnace showed that its peak concentration level in the furnace was two or three times higher than that calculated from the SFA content in coal, assuming that no formation or extinction of the SFA occurs in the region of coal combustion. From these results, we concluded that approximately half of the SFA in the furnace is simply carried over from the submicron coal fragment originally contained (3.5–9.5 wt%) in the pulverized raw coal, and that the remaining SFA is newly formed in the furnace through the breakup of larger coal particles in the devolatilization region. However, the breakup ratio was dependent on the primary air velocity at the burner exit. The percentage of the submicron coal fragment originally contained in the pulverized raw coal that became suspended in the furnace was estimated to be less than 10 wt% under actual flow conditions. The effect of the submicron coal fragment in the pulverized raw coal on the emission of suspended SFA was clearly shown using a small laminar furnace.

Stepwise fragmentation of coal by H 2O 2—trifluoroacetic acid oxidation

An attempt has been made to elucidate the mechanism of oxidative degradation of coal by H 2O 2 in TFA medium. The ‘oxy-coals’ isolated at different stages of degradation have been characterized, and it has been observed that irrespective of the degree of degradation and dissolution, they are similar in respect of elemental analysis and structural parameters ( f a , f har , O COOH, H C , C CH 3 , ring number). This is in sharp contrast to the oxidation of coal by other common oxidizing agents, and is at variance with the earlier claim of Deno that H 2O 2-TFA treatment selectively oxidizes the aromatic part of coal leaving the nonaromatic structures as organic acids in solution. The observations presented herein and those of Deno are possibly complimentary, and an explanation of the overall reaction leading to stepwise degradation and dissolution is attempted. The implications of the findings with regard to the nature of the coal ‘polymer’ and its depolymerization/fragmentation mechanism are also discussed.

Steady advance of coal and gas bursts

This paper establishes a one-dimensional model to analyse the mechanism of coal and gas bursts. It is found that the intrinsic factor governing bursts is the coupling of the initiation of the moving of coal fragments with the gas seepage. A typical (strong) burst can be treated as a steady advance process. The significant dimensionless parameters concerning bursts and an approximate burst criterion are given, and they are in good agreement with the statistics of field data.

Percolation Model for Coal Char Particle Combustion and Fragmentation

Abstract A char combustion model based on percolation theory is developed. The concept of percolation is used to derive the time and position dependent transport and structural properties of the char particle during combustion. By adopting existing kinetic parameters for the surface reaction of the char particle, porosity and oxygen concentration profiles within the particle are calculated for progressive carbon conversion values. Assuming an initially uniform porosity of the char particle, and a Bethe lattice to describe the pore structure, a critical porosity is calculated at which the particle surface layer breaks into fragments. The effects of particle diameter, combustion temperature, pore structure, and fragmentation porosity upon particle reactivity and burnout times are evaluated to determine the sensitivities of the results to the assumption of initial and operating conditions. The impact of fragmentation on the fly ash particle size distribution during pulverized coal combustion is discussed.

Selective spherical agglomeration of coal: An amended mechanism of agglomerate formation and growth and its effect on product quality

The mechanism of agglomerate formation during the selective spherical agglomeration of fine coal with oil was investigated. The effect of agglomerate size on the amount of mineral matter and water entrapped within the agglomerates, i.e. the quality of the final beneficiated product, was also investigated. Scanning electron microscopy (SEM) revealed that during the initial stages small, closely packed agglomerates of coal fragments are formed. Upon further agitation, these primary agglomerates combine into secondary and even tertiary agglomerates. Process water containing liberated mineral matter is trapped between the primary agglomerates which make up the secondary agglomerates. This increases the internal water content and the ash content of the product. It was found that the mineral matter and water content increased with an increase in agglomerate size. The SEM observations were in good agreement with the analytical results.

Hydrocarbon geochemistry of the Puget Sound region—III. Polycyclic aromatic hydrocarbons in sediments

Polycyclic aromatic hydrocarbon (PAH) distributions and sources are characterized in 96 sediment samples from 24 210Pb-dated cores collected at locations in the greater Puget Sound. The highest PAH concentrations are found within a few kilometers of several sources including industrial facilities in northern Puget Sound, urban areas in central Puget Sound, and river systems draining coal-bearing strata. Regional patterns of combustion-derived PAH in surficial sediments indicate little atmospheric or waterborne exchange of PAH between different regions of the Sound. Significant subsurface maxima in combustion-derived PAH concentrations ( 210Pb dated at the 1950s) occur only in sediment cores collected near urban centers. Perylene apparently derives from erosion of a terrestrial source with little or no evidence of in situ production at depth in sediment cores. Coal fragments are carriers of a characteristic suite of alkylated phenanthrene, chrysene, and picene derivatives concentrated near river mouths in central and southern Puget Sound.

Oxygen deficient Ti oxides (natural magn�li phases) from mudstone xenoliths with native iron from Disko, central West Greenland

Mudstone xenoliths in a strongly reduced andesitic subaquatic breccia with native iron from the Asuk Member on Disko contain Ti oxides which are oxygen deficient relative to rutile. Ore microscopy reveals that the mudstone xenoliths contain former clastic oxide grains which have equilibrated to blue Ti oxides and grey aluminous Ti oxides. They also contain still immature coal fragments in a glassy matrix with native iron. The blue oxides are compositionally similar to magneli phases TinO2n−1 within the range n=4 to 7, and several grains contain more than one natural magneli phase. Two other phases found are 1) pale orange blebs in magneli phases with a composition approaching Al1Ti 1 3+ Ti 2 4+ O7 (AlTi phase B) and 2) grey oxide rims on magneli phases or independent grains of the compositional series Al2−x(Ti 0.5 4+ (Mg,Fe)0.5)xTi n−2 4+ O2n−1 with n mostly between 7 and 10 (AlTi phase A). The natural magneli phases equilibrated at oxygen fugacities 4 to 5 log units below the Fe-W oxygen buffer at igneous temperatures and represent the most reduced high-temperature environment yet recorded among native iron bearing rocks from Disko. The extremely reducing conditions were met in rocks where coal fragments were still in a state of degassing hydrocarbon components at the time of quenching. Field geology and carbon barometry indicate equilibration at pressures of less than 10 bars.

Hydrogen-transfer-promoted bond scission initiated by coal fragments

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHydrogen-transfer-promoted bond scission initiated by coal fragmentsDonald F. McMillen, Ripudaman Malhotra, Georgina P. Hum, and Sou Jen ChangCite this: Energy Fuels 1987, 1, 2, 193–198Publication Date (Print):March 1, 1987Publication History Published online1 May 2002Published inissue 1 March 1987https://doi.org/10.1021/ef00002a009RIGHTS & PERMISSIONSArticle Views249Altmetric-Citations67LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (741 KB) Get e-Alerts Get e-Alerts

High-level emplacement of an olivine–dolerite sill into Namurian sediments near Cardenden, Fife

ABSTRACTArchival and recent boreholes over an area of c. 3 km2 have revealed complex magma-host interaction at the termination of an olivine–dolerite sill in Fife. The sill interior has zones rich in plastically deformed, vesiculated heterogeneous sediment surrounded by amygdaloidal basalt. Sediments at the contacts have been reconstituted and enclose blebs of chilled vesicular basalt. Intrusion into low rank coal seams has produced multicomponent tuffisite. A vertically nested and laterally fingered sill front is envisaged as having propagated down dip under a thin cover (<500 m) of wet Namurian sediments. Non-explosive bulk interaction of fluidised sediment and devolatilising magma occurred at intrusive contacts. Steam explosivity was more vigorous where lobes of magma repeatedly intruded moist lignite, to produce compositionally banded tuffisite rich in basalt clasts and coal fragments. The hydrovolcanic explosions did not give rise to surface eruptions because the low volumes of porewater and the high permeability and low tensile strength of the lignite prevented a build-up of high pressure steam.

Prevenance, preservation, and transport of the detrital “coffee grounds” of the Mississippi Delta

Detrital organic fragments or “coffee grounds”, common in the swash zone, and in the lee of barrier islands off the Mississippi Delta consists of up to 40% high-volatile bituminous coal particles of medium to coarse sand size (0.25–1 mm). These coal fragments produce both a well preserved Cretaceous-Paleocene flora and a less well preserved Pottsville (Early Pennsylvanian) flora. This Pottsville flora has close affinities with one described by Kosanke (1950) from the Early Pennsylvanian Illinois Basin coals. If the provenance assignment is correct, these coal particles were transported by the Mississippi River a minimum of 1000 miles from the Interior Coal Province to their present locality in the south Pass area of the Mississippi Delta. However, spillage contamination during a century of barge transport within the Mississippi drainage cannot be ruled out as a possible source for the “coffee grounds” coal. High-volatile coals crop out in the Black Warrior Basin in Alabama to the northeast of the delta. If this is a source of the coal, then an entirely different drainage-transport system would be involved. It would invoke drainage from the Appalachian Province southward, with subsequent longshore current transport, westward — along the Gulf Coast shoreline. Heavy-mineral differences exist between these two sedimentary provinces, with the Appalachian-derived heavy minerals dominated by kyanite, staurolite, and tourmaline; and the Mississippi River Canadian Shield source dominated by amphiboles and pyroxenes. The heavy-mineral assemblage recovered from the “coffee grounds” material is more like those of the Mississippi River Province, and dominated by green hornblende. Vitrinite particles of the coals show no evidence of oxidation rims although they have been in oxygenated waters for an extended period of time during transport. The spore preservation is adequate for specific identification, and is further evidence of minimal oxidation. Coal rank analysis and palynoflora identifications provide a dual approach in reconstructing provenance, transport history, and origin of these detrital organic deposits.

Effects of molten tin catalyst on coal conversion in a hydrogen donor solvent

Catalytic activity of molten tin for the liquefaction of Shin-yubari coal in tetralin solvent was investigated. The catalyst promoted the coal conversion when a small amount of donor solvent was used, while almost no catalytic effect was seen when a large excess of solvent was used. Among conversion data, those for asphaltenes showed most peculiar behavior when plotted against the solvent/coal ratio; a higher and almost constant conversion value was observed for the reaction over molten tin catalyst, while it was strongly dependent upon solvent/coal ratio in the non-catalytic reaction. The effects of reaction temperature on coal conversion with and without molten tin catalyst were also studied using a small amount of solvent. In the non-catalytic reaction the conversion to asphaltenes exhibited a maximum at around 420°C, suggesting that repolymerization of coal fragments became predominant at high temperatures. The temperature for the maximum asphaltene conversion raised to 440°C in the catalytic reaction, showing a radical stabilizing effect of this catalyst. The catalytic behavior of molten tin was also discussed in the light of kinetic analysis.

Determination of transferable hydrogen in coal liquefaction solvents by spectroscopic methods

One of the most important properties of solvents used in direct coal liquefaction processes is their ability to release hydrogen for stabilizing radicals formed by thermolysis. The proposed mechanisms usually involve direct hydrogen transfer reactions between coal fragments and hydroaromatic compounds, which are thereby converted to aromatic structures and/or a hydrogen shuttling reaction. In the latter case, solvent molecules (e.g. PNA) can exchange hydrogen without changing their nature. This paper discusses the n.m.r. and m.s. techniques in relation to a new low voltage mass spectrometric method (l.v.-m.s.) that has been developed.

The roles of vehicle and gaseous hydrogen during short contact time coal liquefaction

The roles of the vehicle and gaseous hydrogen during short contact time liquefaction (SCTL) in microreactors were examined by using a number of synthetic vehicles. The importance of vehicles during SCTL was evaluated on their ability to convert coal to tetrahydrofuran (THF)-soluble products. Reaction conditions were three minutes at 425 °C following a one minute heat-up. Although the consumption of hydrogen (hydrogen donor or gaseous hydrogen) by reactive coal fragments is minimal during the early stages of liquefaction (as in SCTL reactions), hydrogen donors were important and could be ranked according to the extent of conversion to THF-soluble products (tetrahydroquinoline > hydrogenated pyrene > dihydroanthracene = dihydrophenanthrene > tetralin). The importance of gaseous hydrogen was also studied. Gaseous hydrogen was needed if either quality or quantity of hydrogen donor was not adequate in a SCTL reaction. With certain synthetic vehicles, the SCTL stage of an integrated two-stage liquefaction process could be conducted in the absence of hydrogen. Solubility properties that might enhance solubilization of coal-derived products, and therefore the extent of liquefaction, were examined by varying the concentration of certain components ( m-cresol and quinoline) of the synthetic vehicle mixtures. Solubility effects were minimal.

Petroleum heavy oil mixtures as a source of hydrogen in the liquefaction of Cerrejon coal

Petroleum heavy oil and anthracene oil were used as hydrogen donor solvents in a coal liquefaction test. A positive synergistic effect was obtained when mixed (petroleum heavy oil; anthracene oil) solvent was employed. The temperature of maximum conversion was also lower for this mixed solvent than for any of the solvents alone. It is shown from the 1 H n.m.r. spectral data that petroleum heavy oil acts as a hydrogen donor to anthracene oil resulting in hydroaromatic derivatives. These hydroaromatic species donate hydrogen to the coal fragments. The 1 H n.m.r. spectral data allow monitoring of the temperature at which the petroleum heavy oils have maximum donor capacity and consequently the temperature for coal liquefaction in this process.

The occurrence on carboniferous coal of anthropogenic origin in the contemporaneous Vistula river sediments near Cracow (Southern Poland)

AbstractCarboniferous pit coal is the most important anthropogenic component of the contemporaneous Vistula river gravels and sands with individual fractions containing from 10 to 98 per cent coal fragments. Coal concentration is connected with differences in the bulk density between coal and other gravel components. The lower sediments date from the first half of the nineteenth century when the coal began to appear in large quantities in the Vistula channel. The presence of coal is also an indicator of the depth of channel sediment reworking during floods in the nineteenth and twentieth centuries.

Neutron Moisture Meter Calibration for Minespoils Containing Coal

AbstractLaboratory calibrations were used to determine the effect of coal in spoil on neutron moisture meter measurements. Calibrations were conducted on clay loam and loamy sand minespoils from western North Dakota, with and without coal added. Volumetric water contents were overestimated by 3.7% in clay loam containing 8% coal by weight, and 4.7% in loamy sand containing 9% coal by weight using a calibration curve based on similar material without coal. The equivalent water content of the coal (θc) was calculated from the H content of the coal. Correction of calibration curves containing coal by adding θc to volumetric water contents substantially accounted for differences between calibration curves with and without added coal. Due to the large variability in both concentration and size of coal fragments in minespoil, accurate calibration is difficult at best. Since the slope of the calibration curve is unaffected by the presence of coal, changes in soil‐water content over time can be accurately determined from one calibration curve. At sites containing coal fragments, absolute measurements of soil‐water content are difficult, and therefore, only relative differences in water content over time should be determined.

Modeling two-step coal liquefaction processes

The conversion of coal into liquid fuels of increased hydrogen content requires a series of transformations of the original coal structure. These transformations involve both thermal and catalytic reactions that are intrinsically incompatible. Coal conversion occurs first through a thermal decomposition of the coal matrix which requires high temperature. The initial coal fragments are very unstable and tend to recombine unless immediately stabilized either by homogeneous reactions with solvent molecules or through catalytic addition of hydrogen. Catalytic hydrogenation is thermodynamically limited and has poor selectivity at high temperatures, thus immediate transfer of dissolved coal from the high temperature thermal reaction to a lower temperature catalytic reaction is indicated. This paper describes the chemistry involved in the various steps of such conversions and discusses apparatus and techniques that can be used to model these reactions on laboratory scale. The importance of integrating the disciplines of chemistry, engineering, and economics in the evolution of appropriate models is emphasized.

鉄とヨウ素を触媒とした石炭の液化

Taiheiyo coal has been hydrogenated using iron and iodine as catalyst The effect of quantity of iron and iodine, the reaction temperature and reaction time were examined. Catalyst acted very effectively on liquefaction, but the excessive iodine accelerated the condensation reaction decreasing the conversion. Pretty large amount of iodine was trapped in preasphaltene and pyridine insoluble fraction. It is not yet clear how iodine acted on liquefaction or polymerization of coal, however one possible mechanism is as follows. Substitution of iodine affords iodated coal molecules, which produce hydroiodic acid by reacting with molecular hydrogen. Hydroiodic acid thus formed reacts with iron, producing hydrogen radicals which stabilize coal fragment radicals. Condensation reaction takes place between aromatic iodides and other aromatic molecules evolving hydroiodic acid.

Fragmentation behavior of single coal particles in a fluidized bed

The fragmentation behavior of single coal particles has been studied in a small scale fluidized bed for a Kentucky No. 9 bituminous coal. A typical coal particle fragments and swells slightly during devolatilization, producing particles in two distinct size regimes. Although the fragmentation pattern varies from particle to particle, the bimodal mass-based char size distribution obtained for the pyrolysis of a collection of coal particles was found to be little influenced by changes in bed temperature (1023–1123 K), oxygen concentration (0–10%), and coal particle size (2.2–6.2 mm). During oxidation of single coal particles, the dramatic increases in burning rate following particle breakup made it possible to infer fragmentation from the carbon dioxide concentration variation with time of the gas effluent. The number and size of the coal fragments were determined by fitting the CO 2 data with the predictions of a char combustion model. Swelling and fragmentation contribute to an approximately twofold reduction in the average burning time at the experimental conditions studied.