Spontaneous combustion of coal with relation to mining, storage, transportation and utilisation

The phenomenon of spontaneous combustion can be problem where coal is found,nstored or transported. Most studies regarding the spontaneous combustion of coal havenbeen undertaken specifically through study of the situation at the minesite, at points ofnstockpile or utilisation facilities. It is not clear, however, whether there is a relationshipnbetween the propensity of coal to spontaneous combustion as it is moved within anmaterials handling system from the mine through washing and transportation to thenutilisation facilities.nnnnnnnnnnnnn n The main aim of this thesis is to investigate the trend in the liability of a unit coalnto spontaneous combustion within the coal stream from the mine to the utilisation plant.nSeveral tests and experiments have been undertaken to determine the liability of coal tonspontaneous combustion at various points within the coal stream. The major tests were annewly developed qpractical testq for spontaneous combustion, an autoignition test andnspontaneous combustion oven tests. In addition, coal analyses, including petrographic,nproximate and elemental analyses were undertaken to examine the relationship betweennspontaneous combustion and these parameters.nnnnnnnnnnn n The qpractical test apparatusq was developed as a modification of a devicendeveloped by a previous researcher. This apparatus was designed to model the behaviournof a stockpile of large mass and differs from the original apparatus in that the testednsample is in an qas receivedq condition to simulate field conditions closely and to avoidnchanging some parameters, including moisture content, due to sample preparation. This isnone major factor that makes the present study different from previous studies whichnnormally use crushed samples.nnnnnnnnnnnn n The new design for the practical test apparatus is one of the contributions of the lpresent study to spontaneous combustion research. The principle of this test is to measuren1mnthe temperature rise of coal under adiabatic conditions. This is achieved mby passingnregulated rates of airflow through an insulated, vertically mounted, cylindrical tube of 2 mnlength and 200 mm diameter. A comparison of recorded temperature rise of each samplenwas made to determine different liability of tested coals to spontaneous combustion. Details of the apparatus design are provided m the thesis and the results of testsnundertaken are discussed.nnnnnnnnnnn n The autoignition tests and spontaneous combustion oven tests were carried outnusing standard apparatus available in the laboratory. An apparatus developed by Grewernwas used in the autoignition tests. Tested coals and a reference substance were heated innreaction tubes in a furnace at a constant rate of temperature rise with air moving until thencoal temperature reached the reference temperature, established as the autoignitionntemperature. Different autoignition temperatures of the tested coals indicate differentnpropensities to spontaneous combustion. A spontaneous combustion index can bendeveloped using the results of this test.nnnnnnnnnnnnnnnnnnn n In the spontaneous combustion oven tests, the assessment was based on thenanalyses of combustion gases produced from the coal samples when heated gradually in annoven from room temperature up to certain preset temperatures. The relative tendency ofncoal to spontaneous combustion was assessed by comparing the composition of the outletngas stream of each coal sample.nnnnnnnnnnnnnnnnnnnn n The results obtained from the various tests were discussed to determine the trendnin the propensity of coal to spontaneous combustion within the coal flow from the mine tonthe utilisation plant. They were also correlated with the results of the coal analyses to drawnthe relationship between spontaneous combustion of coal and parameters including ashncontent, maceral composition and particle size. The future application of the apparatusndeveloped in this study and the implications of the present study for the coal industry arendiscussed.nnnnnnnnnnnnnnnnnnnnnn n The practical test for spontaneous combustion indicated that coal taken at thenpower station was the most liable to spontaneous combustion, while no substantialndifference was recorded between coal sampled at the washing plant and run of mine. Thenauto ignition test, on the other hand, showed a clear difference in the propensity of testedncoal to spontaneous combustion. Liability of coal to spontaneous combustion from high tonlow is coal taken at the power station followed by that taken at the washing plant and thennrun of mine. In general, the results of the spontaneous combustion oven tests showed thatncoal taken at the power station and run of mine was the most and the least liable tonspontaneous combustion respectively. nnnnnnnnnnnnnnnnnnn n The relationship between spontaneous combustion and maceral analysis showednthat coal with a high vitrinite composition correlates with a high susceptibility tonspontaneous combustion. In contrast, the higher the ash content of coal, the less liable isnspontaneous combustion. The results of the gas analyses to determine the relationshipnbetween spontaneous combustion and coal particle size showed that no consistentnconclusions could be made. However, from sieve analysis it was shown that coal whichnhas the smallest average size was the most susceptible to spontaneous combustion.nSamples of coal were from the Ebenezer and Jeebropilly mines and the Swanbank powernstation, Queensland, Australia.nn