Modelling and parametric investigations on spontaneous heating in coal pile

煤堆自发热模拟与参数研究

Fuel, In Press, Uncorrected Proof, Available online 27 February 2016

Abstract:To predict the spontaneous heating of coal pile by computational fluid dynamics (CFD) is very meaningful for preventing the coal pile from self-ignition. A two-dimensional (2-D) numerical model, which could be simply implemented in FLUENT, was developed in this study. The chemical kinetic parameters of low-temperature oxidation of coal, which were expressed by the outer surface area of particles, were well measured in experiments. The coal piles under different conditions were calculated by using the developed model and measured kinetic parameters, in order to make clear the effects of some important factors. The simulation results indicated the evaporation of moisture from coal played a critical role. The pile height, coal type, wind velocity, and heat loss from bottom have significant effects on the process of spontaneous heating of coal pile. According to these effects, in order to increase the heat loss of pile and then effectively inhibit the self-ignition, the low pile height, good ventilation surrounding the pile, and ground material with high thermal conductivity below the pile should be used. The model developed in this model is expected to become a reliable tool to predict the spontaneous heating of coal pile.

Study of coal oxidation behaviour in re-opened sealed heating

重开密闭发热煤的氧化特性研究

Journal of Loss Prevention in the Process Industries, Volume 40, March 2016, Pages 433-436

Abstract:Possible changes in the oxidation behaviour of coal in the spontaneous combustion site of re-opened sealed heating were studied. Two samples of bituminous coal and three types of coal pre-treatment procedures were applied to simulate in situ conditions at the “spon-com” site: i) pre-oxidation of coal, ii) pre-heating of coal under inert gas, and iii) immersion of pre-heated coal in liquid water. Pre-treated samples were then examined for the production rate of the indication gases evolved during oxidation and for oxidation heat effects. Two main conclusions were drawn with respect to oxidation of the coal inre-opened sealed heating:i) carbon monoxide and unsaturated hydrocarbons maintain their relevance as spontaneous combustion indication gases, however, increased production of both carbon oxides can be expected; ii) coal in the extinguished spontaneous combustion site gains increased susceptibility to the self-heating process.

Effects ofwind barrier designand closed coal storage on spontaneous ignition of coal stockpiles

风屏障设计与封闭煤储对煤堆自燃的影响

Journal of Loss Prevention in the Process Industries, Volume 40, March 2016, Pages 529-536

Abstract:Effects of wind barrier design on spontaneous ignition of coal stockpiles are investigated numerically. A wind barrier changes air flow pattern around a stockpile and spontaneous heating is affected by design factors of a wind barrier. The distance between a wind barrier and a stockpile is selected as a design factor in the stockpile with both a single and a dual barriers and air blowing from the bottom of the stockpile is applied aerodynamically by installation of a wind barrier. As the distance increases, spontaneous ignition is accelerated slightly with a single barrier and significantly with a dual barrier. A dual barrier with longer distance than a critical one doesn't have retard effect any more compared with the stockpile without any barriers. Air blowing induced by a barrier installation is effective when wind speed is higher than a critical one, but partial air blowing is not. Air blowing should be made from the entire domain of the bottom. As a method to root out spontaneous ignition, i.e., free of self-ignition, a closed stockpile is proposed here. Spontaneous heating depends strongly on the size of the silo covering the pile and it is verified that a compact one with a small volume can suppress ignition completely, where maximum temperature in the pile increases initially and finally, falls down below a critical value for self-ignition.

Petrography and mineralogy ofself-burning coal wastesfrom anthracite mining in theEl BierzoCoalfield (NW Spain)

西班牙西北部El Bierzo煤田无烟煤开采过程中所产生的自然煤矸石岩石学与矿物学研究

International Journal of Coal Geology, Volumes 154–155, 15 January 2016, Pages 92-106

Abstract:Coal fires burning around the world over many years have been responsible for the loss of natural resources and also for negative environmental and human-health impacts. Study of self-burning coal wastes based on organic petrology, mineralogy and geochemistry allows the evaluation of factors responsible for the combustion process, and can also be used to assess the changes that are taking place in thermally affected materials. The main goal of this study is to characterize the materials from the Arroyo Galladas, Arroyo Mourin and Fabero coal waste piles, which resulted from coal mining in the El Bierzo Coalfield (NW Spain). Samples of coal, and of unburned and burned or burning coal waste material, were studied by optical microscopy and X-ray powder diffraction (XRD). The results demonstrate that some of the organic matter has preserved its characteristics, but other organic material shows signs of thermal alteration such as cracks, devolatilization vacuoles, dark reaction rims, plasticized edges, and increased or decreased vitrinite reflectance. The resistance of the unaltered organic matter to thermal effects is attributed to the coalification process previously undergone by these coals. The mineralogical composition of the samples indicates that newly formed minerals are present in the burned or burning material, including mullite, cristobalite, cordierite, hematite, jarosite, sanidine, anorthite, sulfur, pyrite, rozenite, coquimbite, tschermigite, boussingaultite and amorphous material. The formation of these minerals is attributed to combustion at maximum temperatures of at least 1100 °C in the Fabero coal waste pile and lower temperatures in the Arroyo Galladas coal waste pile, and to interaction of gases released by combustion with the solid particles, the waters and the atmosphere in and around the waste piles.

Standardization of a method for studying susceptibility of Indian coals to self-heating

印度煤自发热倾向性研究方法的标准化

Arabian Journal of Geosciences, First online: 22 February 2016

Abstract:This paper establishes the standardization of an electro-chemical method called wet oxidation potential (WOP) technique for determining the susceptibility of coal to spontaneous combustion. A total of 78 coal samples collected from 13 different mining companies, spread over most of the Indian Coalfields, have been used for this investigation. Experiments were carried out at different concentrations of KMnO4, viz., 0.05, 0.1, 0.15, and 0.2 N in 1 N KOH and at 27, 40, and 45 °C. With a combination of different concentrations of KMnO4 and temperature, 12 experiments were carried out for each coal sample. Altogether, 936 experiments have been carried out by adopting different experimental conditions to standardize WOP method for wider applications in mining industries. Physical, chemical, and petrographical compositions of coal samples were studied by proximate, ultimate, and petrographic analyses. In order to determine the best combinations of experimental conditions to achieve optimum results in wet oxidation potential method, results were first analyzed by principal component analysis and then by artificial neural network analysis. These analyses clearly reveal that susceptibility index “rate of reduction of potential difference” (RPD12), keeping experimental condition with 0.2 N KMnO4 in 1 N KOH solution at 45 °C, produces optimal results in finding out the susceptibility of coal to spontaneous heating. Further, coals are classified according to their proneness to spontaneous heating with multilayer perceptron (MLP) classifier. A correct classification with accuracy of 94.29 % on test data has been achieved with this classifier. The results have been further validated by tenfold cross-validation method to show its consistent performance over the chosen features.