Theoretical analysis of coal stockpile self-heating
煤堆自发热的理论分析
Fire Safety Journal, Volume 67, July 2014, Pages 107-112
Abstract: This paper theoretically analyses the problem of coal stockpile self-heating under free convection (no wind) conditions. Scale analysis has been used to drive expressions for the stockpile temperature and inflection point (when the stockpile is completely dry) as functions of the key parameters including the coal type, moisture content, and particle diameter as well as the ambient air temperature. Theoretical predictions are then successfully compared with experimental data and CFD simulations results available in the open literature.
Thermal Transformations of Waste Rock at the Starzykowiec Coal Waste Dump, Poland
波兰Starzykowiec煤渣堆矸石的热转化
Coal and Peat Fires: a Global Perspective, 2015, Pages 387-429
Abstract: Large dumps of coal waste are a necessary consequence of coal mining. In some cases, the waste material undergoes self-heating and combustion that changes the nature of the organic- and mineral matter of the wastes. The range of the alterations depends on the properties of the waste rocks (maceral composition and rank of organic matter) and the heating history, especially the rate and duration of heating and the degree of access for air and moisture. The Starzykowiec dump located within Chwałowice coal mine (Upper Silesia, Poland) dates from the beginning of the previous century. It contains wastes that have been thermally altered to varying degrees—reflected in colors ranging from black through yellowish, orange, red, to white and in their structure (some altered wastes are hard and solid, others soft). A coal mud collector is located on the top of the dump. Some of the waste contains organic matter both visible under a microscope and as a bituminous fraction analyzed by GC-MS. Others contain organic matter only visible under a microscope or only a bituminous fraction analyzable by GC-MS or, in some, no organic matter at all. The alterations typically seen in the wastes indicate that the temperature rose slowly; macerals show paler colors, higher reflectance, and no porosity due to devolatilization. In some waste, their yellowish color and very high reflectance indicate a very pronounced degree of alteration. In other strongly altered waste, porous, yellowish organic matter is indicative of high heating rates.
Mineral-matter compositions of the waste on the Starzykowiec dump also show a wide range of thermally induced changes. There are wastes where mineral matter is unchanged and others where primary compositions are completely transformed. High-temperature mineral phases, e.g. diopside, mullite, and indialite, may be formed. On the basis of the color of powdered samples, wastes can be divided into eight groups of different mineral compositions. However, mineral phases such as gypsum and other sulfates formed due to late-stage weathering can change the chemical compositions of the waste. The organic compounds present in dichloromethane extracts, the distributions of which were determined with GC-MS, include n-alkanes, acyclic isoprenoids, pentacyclic triterpanes (hopanes and moretanes), aromatic hydrocarbons together with their C1–C5 alkyl derivatives, and PAHs from naphthalene to perylene. Relative percentage contents of PAHs, and biomarker- and alkyl-PAHs ratios allow waste organic matter composition, geochemical features, and thermal transformations caused by self-heating to be assessed. Several diagnostic changes in biomarker distributions identified include the thermal removal of lighter compounds and related changes in Pr/Ph, MNR, DNR, and TNR values, and enrichment in C31 pentacyclic compared to C30 and C29 triterpanes. Geochemical parameters were correlated to each other and to vitrinite reflectance. Results indicate that biomarker- and aromatic-hydrocarbon parameters, normally applied in the assessment of organic matter thermal maturity, show comparable patterns in the coal waste. Correlations with vitrinite reflectance and between individual geochemical parameters agree with thermal evolution trends typical of coal-waste deposits unchanged by self-heating whereas, in rocks altered by self-heating, biomarker- and aromatic-hydrocarbon parameter values approximate those characterizing overheated organic matter and coal pyrolysates.
The influence of oxygen concentration on the composition of gaseous products occurring during the self-heating of coal and wood sawdust
氧浓度对煤与木锯末自发热产生的气体产物组成的影响
Process Safety and Environmental Protection, Volume 94, March 2015, Pages 463-470
Abstract: This article deals with an assessment of the influence of oxygen concentration on the composition and amount of combustion products generated in the course of heating coal particles and wood sawdust at 150 °C. This was done both with normal air and at 15% oxygen in the air in an isothermal furnace. The generated gases were analyzed by a Fourier Transform infrared spectrometer. Results show that under both conditions, the same substances are formed: water, carbon dioxide, carbon monoxide and aliphatic hydrocarbons. However, the quantities changed. At 21% oxygen, the concentrations of carbon monoxide and methane were higher than at 15% oxygen both in coal and wood. The oxygen concentration was also found to affect the rates of release of CO and CO2. The rate of release of CO was higher at 21% oxygen, but that of CO2 was higher at 15%, indicating two different mechanisms. In all cases, the concentrations of these gases were higher for coal than for wood. The results have implications for the specification of safe conditions of storage of coal and wood substances and the selection of safety measures.
Mutual effects of pyrite and moisture on coal self-heating rates and reaction rate data for pyrite oxidation
黄铁矿与湿度对煤自发热率及黄铁矿氧化反应率数据的相互影响
Fuel, Volume 139, 1 January 2015, Pages 107-114
Abstract: The accelerating effect of reactive pyrite on coal self-heating was measured experimentally using an adiabatic oven. Reaction rate data obtained from the experimental results were applied to a numerical model of coal self-heating. The model results showed reasonable agreement with the measured time taken to reach thermal runaway. However, the shape of the self-heating curves showed subtle variations. Since the pyrite oxidation reaction consumes moisture, there was a mutual effect of accelerated heating as less heat was used up in moisture evaporation.
Comparative mineralogical study of thermally-altered coal-dump waste, natural rocks and the products of laboratory heating experiments
热变质煤渣、天然岩石及实验室加热实验产物的比较矿物学研究
International Journal of Coal Geology, Volume 139, 1 February 2015, Pages 114-141
Abstract: Research on rocks formed due to pyrometamorphism of waste in burning coal-mine dumps (BCMD) mainly in the Upper Silesian Coal Basin has enabled identification of a large number of different mineral species. These species are usually well-known minerals, e.g., olivines, plagioclases and clinopyroxenes. However, their crystal chemistry is often unique. Mineralogical- and chemical similarities between the BCMD and non-anthropogenic geological environments are outlined here. To better understand the crystallization processes of the minerals occurring in the BCMD, three types of heating experiments were performed. For these, ten protolith (thermally-unchanged) dump samples, mostly shales and carbonate rocks, were heated alone and mixed together and with a CaF2 flux. Quantitative chemical analyses of the synthesized mixtures have shown that they are mineralogically similar to the rocks found in the BCMD. They are also similar in terms of their crystal chemistry, e.g., synthesized clinopyroxenes are rich in diopside and esseneite components and may capture phosphorus, plagioclase is rich in anorthite and contains iron and magnesium, and wüstite exists as a solid solution with periclase and is doped with calcium and other elements. Highly variable amounts of indialite–ferroindialite were formed in some samples due to solid-phase transformations or melt crystallization, depending on the experimental conditions and the protolith used.
