Showing papers on "Coal published in 1991"
01 Jan 1991
TL;DR: In this article, an active site concept was proposed to describe the active sites in the process of carbon gasification of coal chars, and the role of these sites in protecting against Oxidation.
Abstract: Chemical Kinetics of Carbon and Char Gasification.- 13C/12C Isotope Spectrometry in the Study of Carbon Reactivity.- Mass Transport and Carbon Reactivity at High Temperature.- Oxidation of Single Char Particles in an Electrodynamic Chamber.- The CO/CO2 Ratio in the Products of the Carbon-Oxygen Reaction.- Oxy-Reactivity of Coal at Low Temperature and High Pressure during Great Depth Underground Gasification Tests.- Forty Years Ago, "La Combustion du Carbone".- Carbon Gasification: the Active Site Concept.- Active Sites and Carbon Gasification Kinetics: Theoretical Treatment and Experimental Results.- Active Sites in Relation to Gasification of Coal Chars.- Specific Reactivities of Pure Carbon of Diverse Origins.- Active Sites in Carbon Gasification with CO2 Transient Kinetic Experiments.- Reactive Surface Area: An Old But New Concept in Carbon Gasification.- Coke Microtexture: One Key for Coke Reactivity.- Thermally Induced Changes in Reactivity of Carbons.- Surface Complexes on Carbon During Oxidation and Gasification.- Applications of Energetic Distributions of Oxygen Surface Complexes to Carbon and Char Reactivity and Characterization.- The Nature of Isothermal Desorption of Carbon - Oxygen Surface Complexes Following Gasification.- Radical Sites as Active Sites in Carbon Addition and Oxidation Reactions at High Temperatures.- Catalytic Gasification of Carbon: Fundamentals and Mechanism.- An Approach to the Mechanism of the CO2-Carbon Gasification Reaction Catalyzed by Calcium.- The Determining Role of Mineral Matter on Gasification Reactivities of Brown Coal Chars.- Protection of Carbon Against Oxidation: Role of the Active Sites.- Inhibition of Carbon Gasification.- Passivation of Carbon Active Sites for Oxidation Protection.- Controlled Gasification of Carbon and Pore Structure Development.- Control of Anode Consumption During Aluminium Electrolysis.- Synthesis and Recommendations for Future Work.- List of Participants.
298 citations
TL;DR: In this paper, a flash distillation analogy is used to explain coal devolatilization, and a new model of coal's chemical constitution, a four-step reaction mechanism, chain statistics, and flash-chain theory is introduced.
Abstract: This theory invokes a new model of coal's chemical constitution, a four-step reaction mechanism, chain statistics, and the flash distillation analogy to explain the devolatilization of various coal types. It is called FLASHCHAIN. The constitution submodel segregates the elements into only four pseudocomponents using the ultimate analysis, the carbon aromaticity and aromatic cluster size from 13 C NMR analysis, the proton aromaticity, and the extract yield in pyridine
264 citations
240 citations
01 Dec 1991
TL;DR: The most convincing evidence of pyrolysis hitherto recognised is the apparent homogenization of xylem cell walls, as seen under SEM and TEM experiments as discussed by the authors, which can be observed in fossil charcoals from both wildfires and laboratory wood charring under controlled conditions.
Abstract: Charcoal is produced by pyrolysis of plant material and its occurrence in the fossil record can be broadly equated with the incidence of palaeowildfire. The past record of such naturally occurring fire, and tha availability of the biomass which represents its fuel, put two constraints on oxygen levels. For combustion of plant material to occur at all requires that the atmospheric oxygen did not drop below a threshold of 13%. Increasing inflammability of plant material at higher oxygen levels suggests that 35% would be a ceiling above which plant biomass would ignite and burn so readily as to be incompatible with sustained forest growth. As we have more or less continuous fossil evidence of forest trees from the Late Devonian onwards, and a similarly sustained record of fossil charcoal from that time to the present (Cope, 1984), this constraints oxygen levels between 13% and 35% over that period (Rabash and Langford, 1968; Watson et al., 1978). However, further experimental work is required to establish the validity of these oxygen values under appropriate conditions and also to sharpen the certainty by which we can discriminate between fusain produced by pyrolysis, and inert wood degradation products produced by other (? biogenic) means. We discuss experiments directed at attempting to establish the validity of physical parameters by which pyrolytically produced fusain can be characterized. The most convincing evidence of pyrolysis hitherto recognised is the apparent homogenization of xylem cell walls, as seen under SEM. Work on charcoal from both wildfires and laboratory wood charring under controlled conditions confirms the homogenization as seen under both SEM and TEM. Controlled temperature experiments show that a further rise in temperature causes the cell walls, initially homogenized, to crack and separate along the site of the middle lamella, giving the charcoal a characteristic fibrous texture. Both of these distinctive phases of response to pyrolysis can be observed in fossil charcoals.
239 citations
TL;DR: In this paper, the authors explain why more oil comes from land derived organic matter disseminated in sediments than from the Carboniferous-Permian coal beds which also are land deposits.
216 citations
TL;DR: In this article, the chemical and thermal responses of six dried coals on exposure to a flow of oxygen or air were studied using isothermal differential thermal analysis (DTA) and temperature-programmed in situ diffuse reflectance infrared Fourier Transform spectroscopy (DRIFTS).
180 citations
KEMA1
TL;DR: The average gas phase concentrations of Hg in the flue gases, based on 33 measurements with no FGD, is 4.1 μg·mfo−3 as discussed by the authors.
Abstract: The Hg concentrations in coal as fired in power plants in the Netherlands are low, 0.2 mg·kg−1 on average. After combustion the Hg is released partly (between 1 and 98%, on average 42%) in a gaseous phase, which is finally emitted into the air. The other part of the Hg, which remains in the ash is separated from the flue gases by electrostatic precipitators. The variation of the vaporisation percentage of Hg is probably caused by the presence of two chemical forms: Hgo and HgCl2. This may be concluded from the observation that relatively high concentrations of HCl in the flue gases (≈150 mg·m−3) give rise to low Hg concentration in the vapor phase. In cases when the concentrations of HCl are relatively low (≈25 mg·m−3) the amount of Hg in the vapor phase is high. The average gas phase concentrations of Hg in the flue gases, based on 33 measurements with no FGD, is 4.1 μg·mfo−3. In a wet FGD based on the lime/limestone-gypsum process 50 to 70% of the Hg in the flue gases is removed, leaving a residual concentration of 1–2 μg·mfo−3. The emission factor is then about 0.5 mg·GJ−1 or 5 μg·kWhr−1. In one particular measuring serie the fate of Hg was studied in a FGD-installation with a prescrubber.
149 citations
TL;DR: In this article, the precursors used in this study were of vegetable and polymeric origin and one activation series based on natural coal was also included, which was used to assess quantitatively the evolution of active carbon properties.
147 citations
TL;DR: In this paper, five processes are investigated for capturing CO 2 from the flue gas of coal-fired power plants, and the captured CO 2 is envisioned to be liquefied at 150 atm, piped to deep ocean, and released through a diffuser.
Abstract: The five processes investigated for capturing CO 2 from the flue gas of coal-fired power plants are (a) combustion of coal in an atmosphere of oxygen and recycled flue gas; (b) scrubbing the flue gas with a recyclable solvent (monoethanolamine); (c) cryogenic CO 2 fractionation of the flue gas; (d) separation of CO 2 by selective membrane diffusion; and (e) scrubbing of the flue gas with seawater. The captured CO 2 is envisioned to be liquefied at 150 atm, piped to deep ocean, and released through a diffuser. Model calculations show that with appropriate release conditions the formed CO 2 drops can be completely dissolved in seawater
126 citations
TL;DR: In this paper, the role of microporous surface area in CO 2 gasification of chars from a sub-bituminous coal was investigated and it was shown that the reaction primarily takes place outside the micropore network on the surfaces of larger pores.
118 citations
TL;DR: In this article, the chemical reactivity of zinc ferrire was studied experimentally to demonstrate the potential use of the zinc ferrite as a sorbent in high-temperature desulfurization of coal gases.
Abstract: The chemical reactivity of zinc ferrire was studied experimentally to demonstrate the potential use of zinc ferrite as a sorbent in high-temperature desulfurization of coal gases. Fifty cycles of H 2 S absorption from simulated coal gas and regeneration under 4.5% oxygen were conducted in a laboratory-scale, packed-bed reactor system simulating gas compositions of a fixed-bed, air-blown gasifier and a regeneration scheme typical of a moving-bed process. Approximately 70% of the theoretical fractional conversion, as determined by thermogravimetric analysis (TGA), was maintained by the sorbent. Less than 1% residual total sulfur and total carbon were measured in the sorbent. Undesired solid phases, (e.g., metal carbides, sulfates, and elemental iron) were absent in the samples as determined by powder X-ray diffraction
TL;DR: In this paper, the effect of pollution on cloud microphysics and its global implications is analyzed to compare the relative effect of a small increase in the consumption rate of oil, coal, or biomass burning on cooling and heating of the atmosphere.
Abstract: The basic theory of the effect of pollution on cloud microphysics and its global implications is applied to compare the relative effect of a small increase in the consumption rate of oil, coal, or biomass burning on cooling and heating of the atmosphere. The characteristics of and evidence for the SO2 induced cooling effect are reviewed. This perturbation analysis approach permits linearization, therefore simplifying the analysis and reducing the number of uncertain parameters. For biomass burning the analysis is restricted to burning associated with deforestation. Predictions of the effect of an increase in oil or coal burning show that within the present conditions the cooling effect from oil and coal burning may range from 0.4 to 8 times the heating effect.
TL;DR: In this paper, a simple equilibrium model for gas composition and yield from coal gasifiers is proposed, which combines mass and energy balances with equilibrium relationships to calculate major and minor species in the produced gas.
TL;DR: For coal or terrestrial (Type III) organic matter to act as a source rock for petroleum, two separate criteria must be met as mentioned in this paper, i.e., coal must be capable of (1) generating hydrocarbons in response to thermal stress (catagenesis) and (2) releasing them to a porous migration conduit or reservoir (expulsion or primary migration).
Journal Article•
TL;DR: In this paper, the adsorptive properties of these carbons, the raw materials used, and the manufacturing processes are outlined. And the high-temperature thermal route (which is the most important for the products employed Ingold recovery) using coconut shells or coal as the raw material is discussed In some detail.
Abstract: After defining activated carbon, the author descriptionbes its structure and outlines the physical characteristics distinguishingone type of activated carbon fromanother. The adsorptive properties of these carbons, the raw materials used, and the manufacturing processes-chemlcal activation, and physical or thermal actlvatlon-are outlined. The high-temperature thermal route (which is the most important for the products employed Ingold recovery) using coconut shells or coal as the raw material is then discussed In some detail.
TL;DR: In coal pyrolysis O-containing structures such as ether bridges and phenolic groups play an important role as mentioned in this paper, and their reactions were studied by non-isothermal pyroplysis of a high volatile bituminous coal and some model polymers with gas Chromatographic detection of the gaseous pyrolys products.
01 Jan 1991
TL;DR: The use of dilute aqueous NaOH solution under mild conditions at atmospheric pressure followed by acid leaching results in a 75 wt% demineralization of the coal as discussed by the authors.
TL;DR: In this paper, the pyrolysis of brown coal samples and bituminous coal maceral concentrates was investigated by non-isothermal thermogravimetry, and the TG data for these coals reveal a two-stage pyroolysis process.
Abstract: The pyrolysis of a suite of brown coal samples and bituminous coal maceral concentrates is investigated by non-isothermal thermogravimetry. The TG data for these coals reveal a two-stage pyrolysis process. The activation energy for the primary pyrolysis stage is considerably higher than that for the secondary pyrolysis stage. It is evident that a particular coal may be characterised by the weighted mean apparent pyrolysis activation energy which correlates with the corresponding specific energy of the coal.
TL;DR: In this article, three basic strategies used by women coal miners to manage sexual harassment are discussed, including casting men into roles as gentlemen and withdrawing socially when they encountered men who behaved as gentlemen.
Abstract: This article discusses three basic strategies used by women coal miners to manage sexual harassment. “Ladies” sought to cast men into roles as gentlemen and withdrew socially when they encountered ...
Book•
01 Nov 1991
TL;DR: In this article, the influence of organic components on coal combustion performance was investigated. But the authors focused on coal quality and did not consider the effect of coal quality on the performance of coal.
Abstract: 1. Introduction. Part A. Coal Characterisation (J.F. Unsworth). 2. Coal Quality and Analysis. 3. Organic Structure. 4. Heteroatoms and Inorganic Impurities. Part B. The Influence of Organic Components on Combustion Performance (J.F. Unsworth and P.T. Roberts). 5. Pulverisation. 6. Pyrolysis. 7. Char Oxidation. 8. Carbon Burn-Out. 9. Flame Stability. Part C. The Influence of Hetero and Inorganic Components on Combustion Performance (D.J. Barratt and J.F. Unsworth). 10. Coal Quality Effects on Boiler Operation and Pollutant Emissions. 11. Prediction of Ash Deposition by Combustion Tests. 12. Ultra-Fine Coal as an Option for Industrial Boilers. 13. The Fate of Fly Ash, Nitrogen and Sulphur. Appendix 1. Analytical details and origin of coals used in our studies. Appendix 2. List of Abbreviations. Author Index. Subject Index.
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TL;DR: In this paper, Coking coal from the Goonyella seam, Australia, was demineralized and three fractions with mineral matter contents of 0.7, 2.9 and 7.9% were obtained.
Abstract: The authors have prepared macroscopic quantities of fullerenes from coke. Coking coal from the Goonyella seam, Australia, was demineralized and three fractions with mineral matter contents of 0.7, 2.9 and 7.9% obtained. Each coal fraction was ground and heated in argon to form rods of coke which were then subjected to electrical arcing at 24V and an a.c. current in a helium atmosphere. The soot was extracted with toluene. Infra-red spectroscopy revealed absorption peaks characteristic of C{sub 60} and C{sub 70} fullerenes in ratios of about 10:1, similar to those reported with graphite as the source. The amount of mineral matter in the coal did not inhibit fullerene formation but affected yield. With 2.9% mineral matter an optimal yield of 8.6% was obtained which compared well with a 9.3% yield from graphite. Further experiments showed d.c. current increased yield. 13 refs., 1 tab.
TL;DR: In this article, a new method was presented for producing molecular sieving carbon (MSC) from coal, where fine ground coal particles were mixed with coal tar pitch, phenol and formaldehyde at 95°C to be agglomerated through the formation of phenol-formaldehyde resin.
TL;DR: In this article, an examination of the reported experiments used to measure the minimum gas temperature at ignition for pulverized coal particles reveals that increasing volatile matter and oxygen concentration has been found to decrease this temperature whereas the effect of particle size appears to depend on the experimental technique.
TL;DR: In this paper, high-resolution P-wave reflection seismology was successfully used to evaluate the risk of an active sinkhole to a main north-south railroad line in an undermined area of southeastern Kansas, USA.
TL;DR: In this article, hydrous pyrolysis experiments were conducted using tertiary lignites (Ro < 035%) from North Dakota and the Far East to evaluate the source rock potential of coal.
TL;DR: This article showed that pre-swelling of bituminous and lower-rank coals with a suitable solvent, followed by removal of the swelling agent, significantly enhances conversion and product quality during subsequent liquefaction.
TL;DR: In this paper, coal and coaly shale samples were analyzed by fluorescence microscopy, Rock-Eval pyrolysis, NMR and NMR, and anhydrous pyrolysate (expelled oil + oil in wash fraction + remaining coal extract) and showed a bimodal n-alkane distribution.
TL;DR: In this paper, a comparison of the TPD pattern of H2S evolution for high-rank coal with those of chars made from lower-rank coals at 400 and 750 °C shows that they are remarkably similar and suggests that the thermal reactions induced in sulphur species in laboratory pyrolysis experiments could be related to those that occur as a result of thermal reactions during coal metamorphism.