Showing papers on "Coal published in 1995"

Aspects of Methane Chemistry

Abstract: As the simplest hydride of carbon and the major constituent of natural gas, methane has attracted increased attention in recent years. An important factor has been the recognition of the significance of world natural gas reserves to energy and chemicals production in the 21st century. This expectation is lined to the gradual depletion of oil reserves and to the possible influence of greenhouse global warming effect on energy policy. The combustion of fossil fuel has caused a rise in the CO{sub 2} level in the atmosphere from an estimated preindustrial level of 280 ppm to the current 360 ppm. If current climate models are correct, this may cause a global warming trend in the next few decades. If public resistance to nuclear energy remains strong, natural gas is likely to become a more important energy source. The low C:H ratio of CH{sub 4} means that on combustion it can furnish a much larger amount of energy per CO{sub 2} molecule released than can oil (approximate ratio, CH{sub 2}) or coal (approximate ratio, CH). This article reviews the occurrence, production, and origin of natural gas and methane. The physical properties, structure, and chemical reactivity of methane are also reviewed. 180 refs.

Environmental aspects of trace elements in coal

Abstract: Preface. 1. General introduction D.J. Swaine, F. Goodarzi. 2. The contents and some related aspects of trace elements in coals D.J. Swaine. 3. Modes of occurrence of environmentally-sensitive trace elements in coal R.B. Finkelman. 4. Geology of trace elements in coal F. Goodarzi. 5. The effects of weathering and natural heating on trace elements of coal F. Goodarzi. 6. The redistribution of trace elements during the beneficiation of coal D.J. Akers. 7. The distribution of trace elements during the combustion of coal R. Meij. 8. The fate of trace elements in emission control systems L.B. Clarke. 9. The transport and dispersion of plumes from tall stacks J.N. Carras. 10. The deposition of trace elements in the environs of a power station W.C. Godbeer, D.J. Swaine. 11. The formation, composition and utilisation of fly ash D.J. Swaine. 12. The leaching of major and trace elements from coal ash D. R. Jones. 13. Microbial influences during mining and usage of coal W.S. Fyfe et al. 14. Mine-land reclamation: the fate of trace elements in arid and semi-arid areas L.P. Gough, R.C. Severson. 15. Overall summary D.J. Swaine, F. Goodarzi.

Experimental Measurement of Coal Matrix Shrinkage Due to Gas Desorption and Implications for Cleat Permeability Increases

Abstract: Coal is not an inert reservoir rock and reacts to gas desorbed from its surface. Coal matrix shrinks as gas is desorbed, increasing cleat width and, therefore, permeability. Very few coal matrix shrinkage data have been reported in the literature so a series of experiments was undertaken to measure such data at reservoir pressures, temperatures, and 100% relative humidity. Strain gages were affixed to the coal sample in the face and butt cleat directions as well as the vertical direction. This work reports measured deformations of a sample of high volatile C bituminous coal from the San Jan Basin during sorption and desorption of first methane then CO 2 . A pressure cycle was also run with helium, a nonsorbing gas, to determine mechanical compliance of the sample. Observed strain gage behaviors are discussed and shrinkage coefficients for both gases reported. Matrix shrinkage was found to correlate with gas content rather than pressure, confirming the work of a previous investigator. Shrinkage coefficients varied more among replicate gages aligned in the same direction than between gages in different directions. Anisotropic shrinkage effects are discussed. Using a matchstick geometry model, equations are derived for permeability change due to matrix shrinkage. Coefficients reported here are used in example calculations of absolute permeability and porosity increases during coalbed depletion.

Modes of occurrence of environmentally· sensitive trace elements in coal

Abstract: Coal utilisation, especially coal combustion, causes the release of many inorganic elements into the environment. Various pollution control procedures and devices are used by the coal industry to minimise the release of these elements. Selective mining and coal cleaning procedures reduce the amount of the inorganic constituents in coal prior to combustion. Electrostatic precipitators, chemical additives, baghouses, and flue-gas scrubbers reduce particulate and element emissions after combustion.

Coal bed methane recovery

Abstract: A process for producing methane from a subterranean coal bed by continuously injecting a carbon dioxide-containing gas into the coal bed and recovering displaced and desorbed methane from a recovery well. The injection gas may be exhaust gas from a hydrocarbon fueled engine.

Thin-film gas sensors based on semiconducting metal oxides

Abstract: In recent years, there has been a gradual realization that an intact environment and properly functioning ecosystems are essential to the continuance of human life; this has led to the tightening up of environmental legislation. As far as air pollution is concerned, gases like sulfur dioxide, the oxides of nitrogen (NO x ), carbon monoxide and carbon dioxide are considered to be the main culprits. Most sulfur dioxide is produced by the combustion of fossil fuels that contain sulfur (coal, oil and natural gas), the sulfur being oxidized to produce sulfur dioxide. This is why SO 2 emissions can only be prevented by chemical binding. Oxides of nitrogen are also produced when fossil fuels are burnt. These oxides are largely the result of reactions between oxygen and nitrogen from the air. The main source of NO 2 emissions is automobiles. In 1986 alone, more than half (2 million tonnes in the former FRG) of all NO x emissions could be directly attributed to this source. In the same year, somewhat less NO x (1 million tonnes in the former FRG) was produced by power stations, distant heating plants and other conversion areas. Air pollution by CO emissions from automobiles is an even more clear-cut case. As CO is produced by the incomplete combustion of fossil fuels, it is not surprising that automobiles alone produced 6.5 million tonnes of this gas in 1986 (former FRG), while the three other user groups (industry/households, trade and business/power stations and distance heating plant, other conversion areas) are only responsible for approximately 2.5 million tonnes (former FRG). The presence of hydrocarbons (CH x ) in exhaust gases is also due to incomplete combustion. Hydrocarbons along with carbon dioxide and water vapour are also considered to be the main causes of the greenhouse effect. With hydrocarbons too, the main source of emissions is the automobile. The emission of CO and CH x from automobiles is particularly abundant when there is an excess of fuel (rich mixture, air coefficient λ<1). The introduction of catalytic converters only provides sufficient recombustion of these components in a very narrow range around λ = 1. Therefore, to obtain the most efficient combustion and the least emission of pollutants, it would seem necessary to monitor the combustion process in each cylinder of a vehicle and to control it so that the exhaust gas expelled from each cylinder has a λ value corresponding to the maximum degree of conversion for the catalytic converter. Fast λ measurements are, therefore, of crucial importance, as they make regulation possible during non-stationary phases of engine operations (starting, braking, acceleration) that account for 80% of the total operating time. Attempts are also being made to introduce combustion regulation in incinerators by means of coefficients. This type of emission would also require sensors that are capable of continuously monitoring the concentration of pollutant components. Sensor elements based on semiconducting metal oxides seem to be promising both for individual cylinder control in automobiles and for monitoring pollutant components

A Laboratory Study of the Partitioning of Trace Elements during Pulverized Coal Combustion

Abstract: The extent of vaporization and subsequent recondensation of many trace elements during coal combustion is believed to depend upon the form of occurrence of the trace element in coal. To test this hypothesis, the forms of occurrence of the trace elements arsenic, mercury, selenium, zinc, chromium, and antimony were determined by successive chemical extractions of both a bituminous and a subbituminous coal. Well-controlled laboratory combustion tests were then conducted, and the concentrations of each element measured as a function of flyash particle size. Results indicated that those elements associated with the coal organic matrix, either ion-exchanged or covalently bound, and those associated with the reactive mineral pyrite were highly volatile. Arsenic, selenium, mercury, and antimony provide examples. In contrast, elements that were associated with silicate or oxide minerals (e.g., chromium) were relatively nonvolatile. For all elements, but particularly zinc, differences in form of occurrence between the two coals led to differences in fraction volatilized. For arsenic and selenium, the results indicated that the condensation pathway was dependent upon flyash chemistry. Using thermochemical equilibrium modeling to interpret the experimental data, it was concluded that arsenic vapors reacted to form calcium arsenates during combustion of the high-calcium subbituminous coal, but condensed as arsenic oxide during combustion of the low-calcium bituminous coal. Limited (calcium) selenate formation was also inferred from the data.

Method for enhanced recovery of coal bed methane

Abstract: A method is disclosed for increasing the methane recovery rate through a wellbore which penetrates a coal seam. The invention utilizes the cavitation of the coal seam surrounding the wellbore after a substantial percentage of the original methane-in-place which is available for recovery from the wellbore has been recovered from the coal seam.

Landsat-TM data for estimating ground temperature and depth of subsurface coal fire in the Jharia coalfield, India

Abstract: Coal fires are a ubiquitous problem in coal-mines, the world over. They burn our prime energy resource, lead to atmospheric pollution and render mining of coal hazardous. Processes leading to coal combustion and spread of subsurface fires are briefly examined in this paper and the role of remote sensing in surveillance of coal fires is presented. The present study aims at developing a quick method for estimating the temperature of the ground surface directly above subsurface coal fires. Utility of TM6 and TM7-band data for temperature estimation is briefly reviewed. It is argued that temperature calculations of surface anomalies related to subsurface fires can only be done on the basis of 8–14 μm band data, due to the low temperatures involved. In the Jharia coalfield, it is noted that subsurface fires in various coal-mines are associated with surface thermal anomalies, as has also been confirmed by ground checks. The pattern of TM6 data distribution and ground truth is used to isolate thermal an...

Coal Flotation with Nonionic Surfactants

Abstract: The flotation response of two high-sulfur coals to a variety of collectors was studied in detail using a 2-liter Denver flotation cell. In comparison with dodecane as the standard oily collector, the introduction of a benzene ring into the oily collector can significantly improve its collecting ability for coal. In our two series of compounds containing oxygenated functional groups, it was necessary to incorporate a benzene ring in the molecular structure in order to have an effective collector without die use of dodecane. The results showed that a much lower dosage of these nonionic surfactants was required to achieve the same coal recovery as compared with dodecane. Most important was the performance of these compounds as promoters for oxidized as well as unoxidized coal. Mechanisms of interaction of these compounds with coal are suggested