Spontaneous Heating Research Articles

固体有機化合物の自動酸化反応活性化エネルギーの分類について 粉体有機物の自然発火の予測を目的として

固体有機化合物の自動酸化反応活性化エネルギーの分類について 粉体有機物の自然発火の予測を目的として

Factors influencing the spontaneous heating of low-rank coals

Two quantities relevant to self heating—activation energy of ignition and thermal diffusivity—have been measured for three different Thai lignites

Applying knowledge-based expert systems to provide guidance for the safe storage of coal

The application of a prototype knowledge-based expert system for spontaneous heating, essh, in surface coal stockpiling operations is described. A brief review of earlier studies concerning the assessment of self-heating risk in stockpiles is presented. Based upon extensive analyses of the incidents of coal storage problems with spontaneous heating, the paper identifies the significant contributory factors which may have caused them. The stacking and precautionary techniques, or the rules of thumb, accumulated from years of experience and research, with particular reference to the safe storage of coal, are also discussed. This high level knowledge is further refined and consolidated into a knowledge-based expert system which aims to replicate the reasoning of human experts in reaching a decision. The system assesses the spontaneous combustion risk by using certainty factor techniques. It is capable of identifying common faults and recommending systematic procedures and methods for inexperienced engineers in handling stockpiles being planned, under construction and in use. Future development of the current system in surface mining operations is highlighted. The approach outlined in this paper offers a new managerial technique and shows how the incidents of spontaneous heating, weathering of coal and environmental impact can be minimized or avoided entirely through appropriate storage and handling, by applying an expert system approach.

A study of spontaneous combustion characteristics of Nigerian coals

The results of a study evaluating the spontaneous combustion characteristics of four Nigerian coals of varying rank are reported in this paper. Crossing point temperature (CPT) and liability index for the four coals were determined. The CPT was found to decrease with increase in coal rank. The liability index, which gives a better evaluation of susceptibility of coal to spontaneous heating, was also found to decrease with increase in rank and with decrease in oxygen content and moisture holding capacity of the coal. Of the four coals studied, the high volatile B bituminous coal had the lowest susceptibility to spontaneous combustion while the subbituminous was the most susceptible.

Effect of coalification on spontaneous combustion of coals

Effect of coalification on spontaneous combustion of coals

Factors affecting the pyrophorisity of spent bleaching clay

Artificial cakes of bleaching clay/vegetable oil have been studied for their pyrophoric character using both Differential Scanning Calorimetry and a constant‐temperature, fixed‐interval, spontaneous heating (CaTFISH) test developed in this laboratory. It was determined that this is a two‐step process involving a first‐stage low‐temperature spontaneous heating reaaction followed by a second‐stage high‐temperature spontaneous heating reaction. The latter is characterized by charring and, in some cases, flaming combustion. A study of relevant variables has established that clay type, filter cake age, oil retention, moisture, and the presence of antioxidant significantly affect the spontaneous heating characteristics of clay/oil masses. Oil type was not found to be a significant variable in these studies.

A knowledge-based system for assessing spontaneous combustion risk in longwall mining

The application of computer technology has achieved considerable success in many parts of the mining industry. However, it has largely been confined to those operations which tend to consist of numerical data and exact algorithms. The knowledge-based system approach has made it possible to build applications which can aid decision making requiring empirical knowledge, subjective judgement, experience as well as uncertain information. The paper describes the development of an expert system for the assessment of spontaneous combustion risk in longwall mining. Previous studies on spontaneous heating risk are briefly reviewed. This application utilizes an expert system shell that combines a powerful inference engine with a user-friendly interface. The system quantifies the severity of self-heating risk in a specific longwall face using certainty factor techniques. The effect of alternative mining parameters on the risk of spontaneous combustion is evaluated such that the mining method can be modified to avoid dangerous combinations. The system also identifies the major factors contributing to the occurrence of self-heating risk and suggests precautionary measures against the potential heating risk. The system has been subjected to hypothetical case studies and the results are encouraging. Further developments of the system are discussed.

Occupational exposure to fungal and actinomycete spores during the handling of wood chips

Abstract Concentrations of airborne spores of fungi and actinomycetes were investigated from 20 samples collected during the handling of wood chips by using a six-stage fractionating impactor (Andersen sampler). Ten samples were taken on wood chip piles or beside the chip conveyor belts of cellulose factories, and ten samples were taken beside chip conveyor belts in central heating plants of saw mills. The spore exposure level varied from 103 to 106 cfu/m3 air. Wood chips used for cellulose production released large numbers of mesophilic and thermotolerant fungi, especially Aspergillus fumigatus, indicating that spontaneous heating had occurred during the storage. By contrast, heavy exposure to Penicillium species and other mesophilic fungi was characteristic of the handling of fuel chips, which are usually only stored for short periods in saw mills. The greatest spore concentration, 3×106 cfu/m3 air (mainly Penicillium), was measured during the handling of fuel chips stored for four months. Heavy exposur...

Investigations on a Theoretical Model and Governing Factors of Spontaneous Heating of Coals on Sea Transportation

<b>Investigations on a Theoretical Model and Governing Factors of </b><b>Spontaneous Heating of Coals on Sea Transportation </b>

An approach to assessing the status of sealed-off fires by examination of fire indices

The advantages and disadvantages of different fire indices in common use, such as CO/O 2 deficiency (def.)%, CO 2/O 2 def.% and CO/CO 2 percentage, as well as those proposed in the literature such as the desorbed hydrocarbon index, the CO—residual gas relationship and the C/H ratio of the products of combustion, are discussed in terms of their applicability for determining the extent and intensity of underground sealed fires. Five cases of different types of fires are studied and examined using the above indices. It is inferred that characterisation of fires should be made from fire indices, such as the C/H ratio, CO/O 2 def.% and the CO/CO 2 percentage, temperature profile studies, pressure differential measurements in stopes and spontaneous heating characteristics of the coal concerned in relation to other mining parameters. Values of C/H ratio above 3 or 4, values of the CO/O 2 def.% of > 0.5 and values of CO/CO 2 of > 2 are indicative of initiation of active fires. A C/H ratio of ⩾ 20 indicates a blazing fire where wooden props may be burning.

炭層内温度の集中監視

The authors conducted the monitoring of the inside temperature of a retained coal pillar at a certain coal mine for the purpose of early detection of spontaneous combustion of coal. The thermometers placed in steel pipes are inserted into the coal every about 20m.The results shows there are some correlations between fire ratio and the monitored temperature. We found that the temperature monitoring is one of the method to help daily gas sampling and analyses. Especially the temperature monitoring is effective for the evaluation of the treatment for spontaneous heating of coal.For the monitoring methods, the sampling interval is required only several times everyday, but flexible interval setting function is recommended for transmitting equipment in case of abnormal situation. The distance of each measuring point is roughly 10-20 m initially, but after monitoring some days, the distance must be reconsidered with the results of monitoring and gas analyses.

The thermal expansion of microcracks and grain boundaries in crystals (I). A new mechanism of crack formation

AbstractApart from known reasons for crack formation it may be effected by the spontaneous microcrack wall heating. This heating takes place because of crack widening and formation of relatively free surfaces (crack walls). These surfaces must have the effective temperature that is well above the temperature in the bulk of crystals, as it has been shown earlier by the author. Simple equations for the thermal expansion of microcracks had been suggested. It has been shown that at the temperature above of 0.9Tm (Tm is the melting point) for the pure metals the spontaneous, without external stresses, crack formation takes place that may cause creep and superplasticity proceeding by the diffusion mechanism. At Tm the spontaneous cracking results in the crystal crushing to the microcrystallites, that is the spontaneous cracking may be considered to be the melting mechanism. From this point of view the intensive thermal expansion of liquids in temperature range from Tm to the critical temperature involves mainly the enlargement of microcrystallite gaps. By using this supposition simple equations for thermal expansion of liquids have been proposed.

Application of wet oxidation processes for the assessment of the spontaneous heating of coal

This paper reports results of wet oxidation of coal by alkaline permanganate solution involving measurements of differential temperature at different base temperatures, at a constant heating rate, and potential changes between a saturated calomel electrode and a carbon electrode immersed in the coal-oxidant mixture within a definite reaction time at a constant temperature. These measurements were made on seven coal samples of known crossing point temperatures (CPT). Four samples, considered to be highly susceptible to spontaneous heating, had CPT in the range 132–137 °C, and three, considered poorly susceptible to spontaneous heating, had values in the range 162–168 °C, showing two distinct zones of correlation between CPT values and the corresponding differential peak temperatures, and between CPT and the observed potential changes. It is suggested that differential temperature and potential difference measurements during wet oxidation of coal may be used as alternative techniques for the assessment of tendency to spontaneous heating.

Seam factor and the spontaneous heating of coal

Previously related publications by the authors have identified the spontaneous heating in underground coal mines as a combination of the seam factor, the geological factor and the mining factor. In this publication the authors pay particular attention to the effects of the seam factor from research conducted from the end of the nineteenth century to the deductions of modern day workers.

Effects of a nonisothermal reactor on ignition and flame-propagation conditions

The ignition mode is important in flame propagation [I, 2]; if the combustion wave is initiated in a hot reactor zone, one can derive the ignition temperature T i if one incorporates the spontaneous heating during the induction AT = T i -To, where To is the wall temperature in the hot zone. AT with the other parameters predetermines whether a diffusion mechanism or a thermal one will predominate in flame propagation [1-4].

Thermally activated release of stored chemical energy in cryogenic media

We have observed very rapid spontaneous heating of the cold solid methane moderator when irradiated by fast neutrons at low temperatures in the Intense Pulsed Neutron Source. In one instance enough heat was released to vaporize a fraction of the methane. We have also induced smaller rapid heat releases —both by slowly warming irradiated methane and by diminishing the effectiveness of cooling. An explanation for these observations is that energy stored in the form of reactive species (H, CH3,...) accumulates in solid methane irradiated at low temperatures, and is released by thermally activated diffusion and subsequent reaction. During irradiation, the density of reactive species can build up sufficiently to become unstable as the rate of heat release due to recombination exceeds the rate of heat loss to the cooled surroundings. Similar effects may occur in other cryogenic moderator materials, and may be responsible for the jets observed from cometary nuclei.

A ‘full-scale’ laboratory test for the spontaneous heating of coal

An apparatus is described which will produce spontaneous heating in a 2 m length of as-mined subbituminous coal, with a moisture content of 18 wt%, without the introduction of any external heat. Preliminary successful results are described, and it is believed that this is the first time that such success has been achieved. Some details of the construction and operation of the apparatus are described. The experiment closely duplicates the full process of one-dimensional spontaneous heating of coal containing its as-mined moisture content. The preliminary results are in good agreement with the one-dimensional model described by Quan.

Combating underground fires in coal mines by direct attack methods

The problems associated with combating underground fires in coal mines are reviewed and examples involving their control by direct attack methods discussed. Special attention is devoted to the digging out and flooding with water methods of fire control. The paper gives a critical overview of practical experiences with fires, especially those originating from spontaneous heating of coal, and concludes with general recommendations to assist in achieving more effective and increased control of such occurrences.

正誤表

正誤表

Statistical appraisal of intrinsic factors affecting spontaneous combustion of coal

This study is concerned with the statistical prediction of the liability of coal to spontaneous combustion. The experimental data consisted of adiabatic oxidation test results on 47 different coals, together with the laboratory evaluation of intrinsic properties of individual coal samples. The measures of propensity of coal to spontaneous combustion was based on the initial rate of heating and total temperature rise in an adiabatic oxidation experiment. These parameters were statistically correlated with various intrinsic properties of coal to isolate the most important intrinsic factors affecting the spontaneous heating potential of coal. A multiple regression analysis between initial rate of heating and total temperature rise and thirteen independent variables have generated a set of equations to predict the liability of coal to spontaneous combustion. It is shown that the predictive equations derived by subdividing the data set according to rank classification can permit accurate prediction of temperature rise, thus evaluating the liability of coal to self-heating. The contribution made by various intrinsic factors to the self-heating potential of coal have also been evaluated by using isolated factor analysis techniques.