Molecular dynamic simulation of spontaneous combustion and pyrolysis of brown coal using ReaxFF
Fuel, Volume 136, 15 November 2014, Pages 326-333
Sanjukta Bhoi, Tamal Banerjee, Kaustubha Mohanty
Abstract:Brown coal is a soft sedimentary organic rock which is complex in nature and is the main source of energy production. In this work, we have studied the combustion and pyrolysis of brown coal using reactive molecular dynamic (MD) simulation. To make the large scale (above 1000 of atoms) reactive system practical, ReaxFF MD system was used which is 100 times faster than the methods of quantum mechanics (QM). To examine the pyrolysis/combustion process and initiation mechanism of brown coal, a fuel lean (ϕ = 2), fuel rich (ϕ = 0.5) and stoichiometric (ϕ = 1) conditions were used in this work. The temperature used was high as per experimental reported condition so as to enable chemical reaction within a computationally affordable time. It was observed that the combustion of brown coal was initialized by thermal degradation subsequently forming small fragments. As the brown coal molecule oxidizes or thermally decomposes, hydrogen is abstracted and reacts with oxygen to form large amount of H2O molecules. Furthermore, the combustion of coal was also studied in the same conditions namely fuel rich, fuel lean and stoichiometric. Potential energy gradually decreases at high temperature while it was the reverse in pyrolysis. It was found that the effects of densities are lesser as compared to temperature. Some important intermediate like formaldehyde (HCHO) generated during the simulation reaction agreed well with the experimental data reported in literature.
Risk and mitigation of self-heating and spontaneous combustion in underground coal storage
Journal of Loss Prevention in the Process Industries, Volume 25, Issue 3, May 2012, Pages 617–622
Juha Sipiläa, d, , , , Pertti Auerkarib, Anna-Mari Heikkiläb, Risto Tuominenb, Iris Velac, Jyrki Itkonena, Mikael Rinned, Kalevi Aaltonend
Abstract:While the self-heating and spontaneous combustion of coal is a known challenge at coal mines and storage sites, there are known methods for mitigating this challenge for typical open stockpile storage. However, closing the storage will reduce access for corrective action, and it is then important to manage the storage and its transport system with added attention without unduly adding cost or hindering availability. This paper aims to discuss the risk, prevention and extinguishing of fires in closed coal storage facilities, particularly in light of the experience with the Salmisaari underground rock storage facility in Finland. The observed autoignition events have indicated an array of contributing factors, some of which are unique to underground silo storage facilities. On the other hand, many features of the storage facilities can be compared with other extant closed storage systems. The factors affecting fire risk are described and the associated fault and event trees are outlined for autoignition at underground storage. Drawing upon the experiences with past events of self-heating and spontaneous combustion, recommendations are given on cost-effective preventive, corrective and other mitigating action for minimising fire risk and promoting storage availability.
Susceptibility of coal to spontaneous combustion verified by modified adiabatic method under conditions of Ostrava–Karvina Coalfield, Czech Republic
Fuel Processing Technology, Volume 113, September 2013, Pages 63-66
V. Zubíček, A. Adamus
Abstract:The susceptibility of coal to spontaneous combustion is a physical–chemical property of coal that can be determined by a laboratory test. A number of laboratory methods verifying the coal susceptibility to spontaneous combustion exist, e.g. the oxidation method under adiabatic conditions, method according to the author Olpinski, method of pulse calorimetry, and CPT (Crossing Point Temperature) method. Any versatile method has not been so far developed, which would become a generally respected and utilized laboratory procedure of objective assessment. The paper deals with the verification of the widely used adiabatic oxidation method. The modification of the method in question consists in the adjustment of the test process by increasing the initial temperature. This procedure enables shortening the test process. Shortening the laboratory test duration creates conditions for wider utilization of the method in practice. The paper presents results of 36 tests of Ostrava–Karvina Coalfield coal samples which confirmed an applicability of the modified adiabatic method in practice.
Characterization of some Indian coals to assess their liability to spontaneous combustion
Fuel, Volume 163, 1 January 2016, Pages 139-147
D.S. Nimaje, D.P. Tripathy
Abstract:Mine fires are a major problem in global coal mining industry and most of them are caused by spontaneous combustion that needs proper attention in strategic planning. The operational management must pay attention to an inbuilt system management for timely detection at the initial stage prior to devastating effect. To assess the spontaneous combustion liability of coal, intrinsic properties and susceptibility indices play a vital role. Forty-nine in-situ coal samples were collected from different coalfields of India. Experimentation of the samples was carried out for proximate, ultimate, and petrographic analysis; crossing point temperature; flammability temperature; Olpinski index; wet oxidation potential analysis; and differential thermal analysis to ascertain the proneness of coal to spontaneous combustion. From the statistical analysis of the samples, it was established that the parameters of the ultimate analysis show significant correlation with Olpinski index as compared to other susceptibility indices and, hence, it can be used as a reliable index to assess the susceptibility of Indian coals to spontaneous combustion.
Petrographic characterization of coals as a tool to detect spontaneous combustion potential
Fuel, Volume 125, 1 June 2014, Pages 173-182
Claudio Avila, Tao Wu, Edward Lester
Abstract:Textural features of 25 worldwide coals were studied after slow oxidation processing (0.5 °C min−1 from 20 to 250 °C in air) using oil immersion microscopy and image analysis techniques. The characterization of samples, before and after oxidation, showed important changes in vitrinite reflectance with high reactive coals, which also related to their intrinsic self-oxidation potential. The morphology of the coal particles was also altered after the oxidation, to produce at least six different morphotypes. Particles with ‘homogeneous change of reflectance’ and particles with ‘oxidation rims’ were predominant in the samples studied, which related to boundary reactive conditions (kinetic and diffusion control of the reaction respectively). These textural characteristics indicate how particles interacted with oxygen at low temperatures, which could be used to predict the most probable pathway during the early stages of oxidation which could then lead to a spontaneous combustion event. The magnitude of the reflectance change and the morphological characteristics of samples studied were also related to the reactivity properties, providing an additional source of information to identify coals prone to spontaneous combustion.
The properties of Çan Basin coals (Çanakkale—Turkey): Spontaneous combustion and combustion by-products
International Journal of Coal Geology, Volume 138, 15 January 2015, Pages 1-15
Gülbin Gürdal, Hakan Hoşgörmez, Doğacan Özcan, Xiao Li, Huidong Liu, Weijiao Song
Abstract:The goals of this study were to investigate the susceptibility of Çan Basin (Çanakkale—Turkey) coals to spontaneous combustion and to determine the composition of the gas produced from the coal during combustion. Coal properties were determined using burned and partly burned coal samples; gas samples were analyzed for their composition. The mineralogical variations of burning coals were also investigated. Our results indicated that the pyrite content of Çan Basin coals is a significant factor for promoting combustion in addition to rank and moisture. X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses indicated that the coal samples contained pyrite, quartz, cristobalite, tridymite, kaolinite, amorphous matter, and gypsum. Fumarolic minerals (sulfur blooming and ammonium chloride) forming on the surface of coal seams were monitored. Elements including beryllium, fluorine, scandium, vanadium, cobalt, nickel, copper, zinc, arsenic, selenium, zirconium, molybdenum, tungsten, mercury, tantalum, lead, and uranium were found to be higher in Çan coal samples than the world average. The concentration of arsenic (max. 3319.7 μg/g) was relatively high and is the major hazardous element in the region.
Gases emitted from coal-fire vents in Çan coalfields were found to consist of a complex mixture of hydrocarbons, greenhouse gases, and toxic concentrations of carbon monoxide (CO), hydrogen sulfide (H2S), and benzene. Hydrocarbon concentrations ranged from 77 to 92%, and the dominant hydrocarbon gas was methane. Ethane (0.3 to 2.1%) and propane (0.2 to 1.4%) were also detected. Hazardous compounds such as 5-methyl-3-propyl-1,2-oxazole (C7H11NO), ethanediimidic acid, 1,2-dihydrazide (C2H8N6), and 2,3-dihydrofuran (C4H6O); high concentrations of nitrogen (N2) (max. 6.8%) and carbon dioxide (CO2) (max. 18.2%); and low concentrations of carbon monoxide were also determined. Greenhouse gases (CO2 and methane (CH4)) from burning coal beds may contribute to climate change and alter ecosystems. Gas components including furan, H2S, CO, carbon disulfide (CS2), benzene etc., can be hazardous to human health, even in trace amounts. As a result, the uncontrolled release of pollutants from burning coal beds presents potential environmental and human health hazards.
