Comparison of methods for the determination of organic oxygen in coals

Coals distributed widely in rank and geographical origin have been analysed for organically-bound oxygen by several conventional and fast neutron activation analysis (FNAA) techniques. Pyrolysis of demineralized coal with measurement of evolved CO₂ by coulometry was found to be the most reliable of the conventional methods. Direct FNAA determinations of organic oxygen by analyses of demineralized coal (DMC) samples yielded data in excellent agreement with pyrolysis, as did values computed using a modified ‘by difference’ calculation. The convergence of data from these totally independent approaches, suggests a measure of true organic oxygen levels has been achieved. A ‘difference method’ based on FNAA determinations of total dry coal oxygen and inorganic oxygen in low temperature ash yielded organic oxygen data that were typically lower than pyrolysis values, possibly due to oxidation of organic sulphur in the ashing process and/or the presence of non-extractable mineral oxygen in the DMC used in the pyrolysis method. A third FNAA ‘difference method’ based on simultaneous determinations of both total oxygen and silicon contents of dry whole coals, followed by estimation of the inorganic oxygen contents based on the silicon contents, was found to be rapid and adaptable to on-stream analysis. However, observed mineralogy-dependent deviations from a simple inorganic oxygen-silicon relationship suggest that the latter technique would be most successful when applied to coals with similar mineralogy.     

Bacterial removal of sulphur from three different coals

Three different types of coal were taken for microbial desulphurisation experiments using isolated cultures of Thiobacillus ferrooxidans. The samples were milled and then sieved. The effect of various parameters on microbial desulphurisation of three different coals such as particle size, pH, pulp density, media composition and contact time was studied. The conditions were optimised for the maximum removal of sulphur (91.81 wt% for Rajasthan lignite, 63.17 wt% for Polish bituminous coal and only 9.41 wt% of Assam coal).     

Sulphur transformation and removal for Western Kentucky coals

Inhibition isotherms were measured for Western Kentucky No.9 coal. Crushed and sieved coal (?25 + 140 U.S. mesh) was fluidized in 10-g batches in a 22-mm i.d. quartz reactor up to a temperature of 870 °C. The release of hydrogen sulphide during heatup under nitrogen and at the run temperature (usually 1–2 h) under the same gas (pyrolysis), hydrogen, or hydrogen/hydrogen sulphide mixtures was followed by gas chromatography. The residue or char was analysed for pyritic, organic, sulphide, sulphate, and total sulphur. Inhibition isotherms, which are pseudo-equilibria between sulphur in the char and gaseous hydrogen sulphide, were measured at 600 and 870 °C. At the lower temperature the isotherm was found to be independent of the hydrogen sulphide concentration in the gas stream and the char sulphur content remained constant at 2.6%. At 870 °C the sulphur content of the char was greater than that of the original coal when gas mixtures of 1, 3, and 6% hydrogen sulphide in hydrogen were used, indicating the necessity of maintaining low hydrogen sulphide concentration for sulphur removal. In pure hydrogen, sulphur removal increased continuously from 47% at 600 °C to 84% at 870 °C. For pyrolysis under nitrogen, sulphur removal was 40% at 600 °C and increased to 59% at 740 °C. No further removal occurred above this temperature up to 870 °C. In addition to the inhibition isotherms, sulphur-form transformation diagrams were constructed for coal treated with nitrogen, hydrogen, and hydrogen/hydrogen sulphide mixtures. Pyritic sulphur, which comprised 40% of the sulphur in the original coal, was completely converted to ferrous sulphide at 600 °C in hydrogen and 740 °C in nitrogen. At 870 °C the sulphur content of the char produced under hydrogen was 1.1% made up of 48.4% ferrous sulphide, 43.4% organic sulphur, and 8.2% sulphate.     

Scale-up of an electrochemical cell for oxygen removal from water

In a previous paper an electrochemical method for the removal of dissolved oxygen from water was described. In that work the oxygen-rich water was passed through a three-dimensional cathode and the dissolved oxygen was reduced on the cathode surface to water. In the present study electrochemical oxygen removal and, especially, the scale-up of the deoxygenation cell were investigated. The volume of the three-dimensional cathode was enlarged and suitable cathode materials and membranes were tested. The maximum flow rate and the optimum cell voltage were determined. Finally, two cathodes were connected in parallel flow. A flow rate ten times higher than that of the former laboratory-scale cell was achieved. Over 99.95% of the dissolved oxygen was removed. No significant amount of by-products, hydrogen or hydrogen peroxide, was observed.Nomenclature A area of the membrane (m²) - D hydrodynamic permeability (g s^–1 m^–2 bar^–1) - F Faraday number (96 500 A s mol^–1) - I current (A) - I _meas measured current (A) - I _theor theoretical current (A) - M _i molecular mass of species i (g mol^–1) - flow rate (g[water] s^–1) - m _de mass of water decomposed on the anode (g) meomass of water transported through the membrane by the electroosmosis (g) - m _ev mass of water evaporated with the gaseous oxygen (g) - m _p mass of water transported through the membrane due to the pressure (g) - m _tot total mass change of the anolyte (g) - N _w water transference number (2.2) - p pressure of the gas bubble (pressure of the air, 101 300 Pa) - pH₂O water vapour pressure at room temperature (3000 Pa) - P pressure difference between catholyte and anolyte (bar) - [O₂] mass fraction of dissolved oxygen (g[O₂] g[water]^–1) - t time (s) - z _i number of electrons needed per species i     

Determination of organic oxygen content of coals

Fast neutron activation analysis has been used to determine organic oxygen (O_org) content of coals by subtracting the oxygen content of the mineral matter from the total oxygen content of the coals. Mineral matter was isolated by low temperature ashing in an oxygen plasma. Optimum ashing conditions produce minimal changes in chemical composition of mineral matter; these changes were taken into account when calculating the O_org content. The O_org contents of whole coals are substantially different — in some cases by as much as 47% — from the ASTM oxygen contents and those calculated on a dry, mineral matter free basis from the ultimate analysis data. Excellent agreement between the FNAA O_org contents of the whole and demineralized coals lends support to the reliability of this experimental approach.     

Electrochemical removal of dissolved oxygen from water

A new electrochemical method of oxygen removal has been developed in which oxygen-rich water flows through the three-dimensional cathode of an electrochemical cell. The cathode removes the dissolved oxygen from the water and the anode releases it as gas into the air. By this technique oxygen levels lower than 3 µmg oxygen per kilogram of water can be reached (starting level: oxygen-saturated water, 8000 µg kg^–1). This result is better than that obtained by physical methods and is equal to those obtained by chemical methods. Compared with conventional methods, the advantages of the electrochemical method are high effIciency, low energy consumption and avoidance of the use of toxic deoxygenation chemicals.     

开滦矿区入选原煤中的硫态分布及降硫措施

介绍了开滦矿区煤层硫分及各矿入选原煤硫分赋存情况 ;针对开滦入洗原煤可选性差、硫分偏高的特点 ,为满足用户对精煤硫分要求 ,提出了三种降低精煤硫分的措施 ,并对其可行性进行了初步探讨。     

Effect of inorganic matter removal from coals and chars on their surface areas

Removal of inorganic matter from coals by acid treatment brings about random and, in some cases, significant changes in surface areas measured by adsorption of N₂ and CO₂. Changes in surface areas of chars are generally more pronounced than those found in coals. However, the surface area changes in chars are markedly dependent upon whether the acid treatment is given to the coal precursor prior to charring or to the char produced from the raw coal. Changes in surface areas of raw coals and chars produced therefrom have been attributed to: (i) ‘physical’ removal of inorganic matter from the aperture-cavity system, (ii) bonding of HCl to basic nitrogen present in pyridine-like structures, and (iii) adsorption of acid. Results suggest that the removal of inorganic matter from coals prior to charring affects the carbonization process and, hence, the surface area of the resultant char.     

锅炉给水除氧技术新进展

锅炉给水除氧是防止热力系统腐蚀的重要方法。本文分析了常用的物理除氧和化学除氧的优缺点,介绍了当前除氧技术研究的最新进展,详细描述了触媒型钯树脂催化加氢除氧和光催化加氢除氧技术,并对除氧技术的发展加以展望。     

常用焦化废水中氨氮去除方法的比较

介绍了焦化废水脱氮处理方法,包括物理法、化学法、物理化学法以及生物法,比较了各种处理方法的优缺点。认为生物脱氮技术处理效果较好,工艺稳定、处理成本低,是目前工程设计中应优先考虑的脱氮工艺,其中A/O、A2/O已成熟,而其它工艺有待进一步研究发展。同时认为研制出无二次污染、操作简便、性能稳定、运行成本低的处理技术是今后的发展方向。     

Modification of vitrinite coals in a low-temperature oxygen plasma

Transformations in the organic matter of vitrinites in coals of various ranks as a result of their interaction with oxygen activated in an RF field were characterized using IR spectroscopy and solvent extraction.     

Modification of Mongolian coals using a low-temperature oxygen plasma

The results of a study of the effect of the treatment of coals from the Khar Tarvagatai, Nuurst Khotgor, and Khushuut deposits of Mongolia in a low-temperature oxygen plasma are presented in this article.     

Investigation of the flash pyrolysis of some coals

Five bituminous coals, an anthracite and a lignite have been flash-pyrolysed by the electrically-heated grid technique or by means of an electrically-heated fluidized-bed. In the experiments using a heated grid, data were obtained on rates of rapid devolatilization and on the composition of the gases and tars evolved with heating rates up to 3000 Ks^?1 and peak temperatures up to 1400 K. Similar, but more limited data were obtained using the fluidized-bed system. Mathematical models based on overall single- or two-reaction pathways were compared with the experimental results. Good agreement could be achieved by the latter with activation energies of 16 and 35 kJ mol^?1.     

Liquid-phase adsorption of phenol by activated carbons prepared from bituminous coals with different oxygen contents

Activated carbons prepared from two bituminous coals were used to adsorb phenol in aqueous solutions. The major difference between the coal precursors is the oxygen content. The carbon preparation consisted of carbonization of the coals followed by activation in CO ₂ to various extents of burn-off. Experimental results show that the amount of phenol adsorbed generally increases with the BET surface area of the carbon. The carbons prepared from the coal with a higher oxygen content have larger surface areas, and, therefore, exhibit higher capacities for phenol. The surface area of the carbon increases with the extent of carbon burn-off, whereas the increase in the adsorptive capacity due to the increasing burn-off level does not show a linear relationship with the increase in area; the ratio of the capacity to BET surface area is not constant and decreases with the burn-off level. This has been attributed to the accessibility of phenol to the surface being affected by the length of diffusion path, which is an increasing function of the burn-off level or the particle size. The amount of phenol adsorbed decreases with the temperature for these carbons. It was found, according to the Langmuir model, that the adsorption process was significantly affected by the oxygen content in the coal precursors. © 1999 Society of Chemical Industry     

Sorption removal of oxygen by refractory materials from iron-nickel melts

Conclusions It is shown that it is possible in principle to carry out the sorption deoxygenation of a metal by refractories. A highly developed surface helps to provide a more complete sorption deoxygenation.Experimentally, periclase has better sorption properties than corundum.Most of the oxygen is removed from the melt in the first 5–10 min. The extent of the oxygen removal from the melt increases with an increase in its original concentration.Translated from Ogneupory, No. 3, pp. 22–24, March, 1984.     

Electrolytic removal of oxygen from gases by means of solid electrolyte

Nitrogen gas, containing controlled amounts of free oxygen and water or carbon dioxide, was de-oxidized by means of a solid oxide electrolyte tube at temperatures from 800 to 1000°C and at applied voltages of 0.5–3.0 V. The oxygen potential of the resulting gas mixture was measured simultaneously. The efficiency of the removal of oxygen, present in free or combined state, is shown as a function of the initial oxygen content , temperature and applied voltage. The electrolysing current/applied voltage relationships obtained indicate that the resistance of the electrolysing circuit is mainly determined by the initial free oxygen content of the gas mixture. The behaviour of solid oxide electrolytes with externally applied potentials corresponding to pure ionic and mixed conduction is also discussed.     

Electrocatalytic removal of dissolved oxygen from seawater in a packed-bed electrode

Oxygen dissolved in seawater is the source of severe corrosion issues in off-shore platforms for oil exploitation. The electrocatalytic reduction of dissolved oxygen from seawater was investigated at laboratory scale as an alternative to the current processes for the removal of oxygen. Due to the low concentration of dissolved oxygen and the very high conversion required before use of seawater in off-shore platforms, the reduction has been carried out in a packed–bed electrode consisting of carbon-based particles of various nature. The reduction involves the intermediate formation of peroxide species whose further reduction into hydroxyl ion is a slow process on Pt-free surfaces. A continuous laboratory packed-bed electrode was designed and tested in long-term operations for the assessment of the production and the reaction selectivity. The removal of oxygen from seawater can be inhibited by the formation of a solid CaCO₃–Mg(OH)₂ film at the carbon particles, which favours the accumulation of peroxide species. However, this electrode deactivation can be avoided at sufficient polarisation.     

Carbons prepared from coals for anodes of lithium-ion cells

Carbons were prepared by pyrolysing eight different coals from the Argonne Premium coal sample bank at temperatures near 1000 °C. Electrochemical cells were made to study lithium insertion in these carbons. The electrochemical behavior and physical properties of these pyrolysed coals was compared to that of pyrolysed sugar, PVC and pitch which we have studied carefully before. Using powder X-ray diffraction and small angle X-ray scattering (SAXS), we show that pyrolysed coals which have the smallest fraction of parallel-stacked graphene layers and hence the largest number of nanoscopic pores per unit mass, have the largest capacity for lithium insertion. A reversible capacity of about 450 mAh/g was attained for lithium/carbon cells made from Blind Canyon Seam coal.     

Conversion of non-coking coals to coking coals by thermal hydrogenation

Coking properties are observed in four non-coking coals, a lignite, a subbituminous coal, a semianthracite and an oxidized bituminous coal which had been treated by partial thermal hydrogenation. The effects of temperature, reaction time and hydrogen pressure on liquid and solid product yields are examined. Microscopic examination of the hydrogenated solid residues shows that they all contain structures somewhat spherical in shape which are associated with mesophase development. The dilatation, plastic character and free swelling index of the hydrogenated solid products were considerably better than those of the original coals. Dilatation residues produced from hydrogenated solids exhibited anisotropic structures.     

Diffusion models for gas production from coals: Application to methane content determination

Experimental studies of methane diffusion from coal cuttings have been analysed with both a unipore diffusion model and a bi-disperse pore structure diffusion model to determine the time range of each model's validity. Initial desorption, during the first 50% of volume desorbed, can be adequately described by the unipore model. For Fruitland coals of the San Juan Basin, the unipore diffusion coefficient varied by less than a factor of 2 from a value of 1 × 10^?5s^?1 despite large variations in sample depth and location. The unipore diffusion model has been successfully incorporated into a lost-gas-correction-factor determination as part of a new technique to delineate coal-bed methane. To describe methane diffusion over the full timescale of desorption, a more complex model which more accurately represents the observed bi-disperse pore structure of coal is required. Using that model the observed desorption rate is described over all the desorption. This model is especially applicable as a source term in describing overall well production.