Thermal Characteristics and Evolution Model of Coal Fire at Surface and Underground Coal Mine

露天与地下煤矿煤火热特征及其演化模型

Procedia Chemistry, Volume 19, 2016, Pages 687-693

Teuku Andika Rama Putra

Abstract:Many surface or underground coal fires are believed to exist worldwide. They keep burning and extend the areafor many years more. The main objective of the study is to gain fundamental understanding of coal fire thermal characteristics and to design the thermal evolution model. Fire propagation over periods of time were analyzed and the model assists to locate the fire zone areas indicated by the temperature changes and other thermal related variables of natural burning coal so that it can be used to develop the predictive model dynamic of burning front. The model is crucial for spontaneous coal combustion prevention study which responsible for many coal mine accidents. Burning coal involved complicated and complex processes that are difficult to predict. The methodology is modeling coal as a physical process of a porous media (heat transfer in a porous media) and heat transfer in fluids. The dynamic burning front of coal fire simulation will be carried out using COMSOL Multi-physic®. The process is mainly the coal oxidation during the low and high temperature. The typical chemical reaction of the coal decomposition is shown as C156 H74 O30 N2S2→138C + 12CO2 + 6CO + 37H2 + N2 + S2. The thermal evolution model was determined to be the coupled conduction and convection heat transfer phenomena. The temperature changes and fire propagate after the simulation along the coal cylinder model. The study found that by increasing the heat flux and the prescribed temperature, it will increase the temperature gradient and the distribution of temperature from the heat flux inward.

Impact of underground coal fire on coal petrographic properties of high volatile bituminous coals: A case study from coal fire zone No. 3.2 in the Wuda Coalfield, Inner Mongolia Autonomous Region, North China

地下煤火对高挥发分烟煤煤岩特性的影响：中国内蒙古乌达煤田3.2号煤火区实例研究

International Journal of Coal Geology, Volume 171, 15 February 2017, Pages 185-211

J. Kus

Abstract: The Wuda Coalfield located in the Inner Mongolia Autonomous Region, North China is known as one of China's major source of prime coking coals and a site of well-researched and well-documented underground coal fires. The underground coal fire at the coal fire zone No. 3.2 is situated in the active coal mine of Suhai-Tu, located in the north westerly part of the Wuda Coalfield.

The present paper investigates the impact of the underground coal fire on the coal seam No. 10 by application of coal petrographic methods, including detailed characteristic of macerals and other coal components, maceral analysis, microstructural analysis, and vitrinite reflectances performed on (1) coal grains lacking impurities, microfractures, dark oxidation rims, (2) on dark-rimmed vitrinite, as well as (3) on low-temperature semi-coke. The investigated coal seam No. 10 represents a high volatile A bituminous coal and is dominated by vitrinite, followed by inertinite with minor amounts of liptinite and by non-isotropic low-temperature semi-coke. The microstructure of the oxidatively and thermally altered coals is represented by (1) extensive non-tectonic microfissures and non-tectonic microfractures i.e., shrinkage microfractures, leading to defragmentation of coal grains, (2) dark oxidation rims observed at grain margins, non-tectonic microfissures and microfractures, and by (3) devolatilisation micropores. Random vitrinite reflectances measured in (1) coal grains lacking impurities, microfractures, and dark oxidation rims, and in (2) dark-rimmed vitrinite at non-tectonic microfissures and fractures reveal significant lateral variations. The presence of low-temperature semi-coke and its marked lower reflectance values are indicative of thermal alteration induced by the underground coal fire in the coal fire zone No. 3.2. The results obtained from the performed analyses of organic matter point to both low-temperature oxidation and low-temperature-pyrolysis processes. The applied coal petrological approach revealed characteristic changes to the coal's microstructure, its petrographic composition, as well as to optical properties induced by the underground coal fire.

Oxidatively and thermally altered high-volatile bituminous coals in high-temperature coal fire zone No. 8 of the Wuda Coalfield (North China)

中国乌达煤田8号高温煤火区热氧化影响的高挥发分烟煤

International Journal of Coal Geology, Volumes 176–177, May 2017, Pages 8-35

Jolanta Kus

Abstract:Coal fires have received increasing attention due to their environmental, economic, and social impacts. Their significant influence on coal properties is widely documented by geophysical and geochemical methods.

The present paper demonstrates, by means of coal petrological methods, significant changes of microstructure, optical appearance, and optical properties of medium-rank (bituminous) coals affected by an underground coal fire. The studied changes are suggested to result from distinct oxidative and thermal alterations induced by a high-temperature regime (temperatures over 800 °C) encountered in the coal fire zone No. 8, Wuda Coalfield. The investigated coal seam No. 9 represents a high volatile A bituminous coal and is dominated by vitrinite, followed by inertinite with minor amounts of liptinite. The microstructure of the coal-fire affected coals facilitate a broad spectrum of characteristic features. The microscopic analyses revealed development of (1) non-tectonic fissures and non-tectonic fractures, (2) distinct micropores, (3) dark oxidations rims, and (4) bright spots interpreted as incipient mesophases. Optical properties were characterised for megasporinite and vitrinite. In the examined megasporinite a noticeable anisotropy and distinct granular appearance was observed. In the investigated coals both a dominant increase as well as a minor decrease in both random and maximum vitrinite reflectances were documented for (1) coal grains and (2) dark-rimmed vitrinite at non-tectonic fissures and non-tectonic fractures. In addition, also a characteristic bimodal vitrinite population was measured. The increase in bireflectance was clearly documented for two sub-zones within the coal fire zone No. 8. The applied Kilby's cross-plots suggested a large overlapping of the data sets of R'max and R'min, indicating marked changes in vitrinite structure. The applied coal petrological approach revealed distinct changes to the coal's microstructure, appearance, as well as to optical properties induced by the underground coal fire. The presented coal petrographic approach may help determine the extent of coal fires in coal mines and the direction of propagation of coal fire front.