Risk Of Spontaneous Combustion Research Articles

Research on Relationship Between Porosity of Coal, Amount of Air Leakage and Gradient of Wind Pressure

Abstract About half of China's underground mining coal seams have risks of spontaneous combustion, and the condition of airflow in coal directly influences coal's nature of spontaneous combustion. In the experiment, through putting pulverized coal of certain porosity into ventilating tube and attracting wind with pipe-type ventilator at an end, the differential pressure of both ends of the ventilating tube and the ventilating volume in tube are determined. Results of experiment show that the ratio of gradient of wind pressure and amount of air leakage per unit area is stationary for coal sample of certain porosity. In the process of porosity increasing from 0.4 to 0.6 and corresponding p/q increasing from 7.248 2 to 1 840.4, as long as any one of value of p/q and porosity is fixed, the other one can be fixed. This has certain referencing value for further improving the theory of spontaneous combustion of coal and preventing technology against spontaneous combustion of coal.

Division of Spontaneous Combustion “Three-zone” in Goaf of Fully Mechanized Coal Face with Big Dip and Hard Roof

The risk of spontaneous combustion in goaf of fully mechanized coal face with big dip and hard roof is high, and gas monitoring is more difficult. The method of dividing spontaneous combustion “three-zone” by temperature rise and CO concentration in goaf was presented in this paper. Tubes and temperature probes were buried in goaf at NO.7162 fully mechanized coal face in Longdong Coal Mine to monitor the temperature and gas concentration in goaf. The regularity of temperature and gas concentration changing with the advancing face was analyzed. According to the change of temperature and CO concentration in goaf, the range of spontaneous combustion “three-zone” was determined and verified by oxygen concentration. The method of dividing “three-zone” by temperature rise and CO concentration is simple, accurate and reliable, and provides scientific basis for spontaneous combustion prevention in goaf.

An investigation of the factors associated with interpretation of mine atmosphere for spontaneous combustion in coal mines

The risk of spontaneous combustion of coal is highly serious especially in gaseous underground coal mines. In many cases such a spontaneous combustion is a source of initiation of methane-explosive mixture with tragic consequences. Early indication of spontaneous combustion and determination of its seat temperature is in a given environment a key part of safety of underground coal mines. A commonly used method for the detection of spontaneous combustion is an interpretation of coal oxidation gas products whose historical roots go back to the first halve of the 20th century as Graham's ratio. In the second half of this century a wide research on application of desorbed higher hydrocarbons C1–C4 and hydrogen for the given purpose took place. Until now, the interpretations in question encounter significant inaccuracies. The paper describes the research on factors affecting the accuracy of the determination of coal spontaneous combustion temperature on conditions of underground coal mines. The research was focused on the accuracy of interpretation of mine gases in connection with the use of laboratory verified gas characteristics of thermal oxidation of coal. Three chromatograph laboratories had been involved to test thermal oxidation of coal to determine a deviation of spontaneous combustion gases. The variability among the laboratories and used techniques were insignificant. Besides the laboratory methods, it may not reflect processes in coal mines and one of the results was that coal itself had been a source of substantial variability of desorption of spontaneous combustion gases. The spontaneous combustion data still requires human interpretation. Simple criteria for providing warning by a computer do not exist just yet.

Holistic management of sulphides at Rio Tinto Iron Ore's Pilbara mine sites

Rio Tinto Iron Ore (RTIO) manages eleven mines in the Pilbara region, Western Australia. Three of these mines have previously or are currently mining black shale that contains varying amounts of pyrite. Several new deposits currently being evaluated and existing mines that may progress below water table in the future, will also encounter this waste material. The black shale presents not just an acid rock drainage risk but also a spontaneous combustion risk. This paper presents the black shale management strategy and provides an overview of the relevant activities undertaken by RTIO. The strategy can be divided into two components which firstly involve defining the risk and secondly involve managing the risk. The mineral waste management plan is used to identify specific mineral waste hazards by:•geochemical characterisation of waste material,•undertaking mine site specific risk assessments,•characterising the receiving environment,•identifying sulfidic boundaries in geological and mining models,•quantifying the amount of sulfidic material in medium and long-term mine plans, and•designing and sequencing black shale waste dumps.Once a mine exposes black shale the Spontaneous Combustion and Acid Rock Drainage management plan is used and the major activities are:•regular site meetings with a representative from every group that works with black shale;•compliance with safe working procedures for site specific and detailed activities;•regular training;•the use of specific explosives to prevent premature detonation;•ongoing geochemical characterisation;•acid water management, monitoring and analysis;•regular internal and external auditing of procedures and practices; and•closure planning assessments and preparations (ie cover trials, geochemical void modelling, geochemical waste dump modelling).The success of this holistic strategy is evident by the awareness of personnel within the business, thorough understanding of the geochemistry and by undertaking proactive management of black shale during mining. The strategy and management plans adopted by Rio Tinto Iron Ore have activities that other mine sites with potentially acid forming material may like to consider implementing.

Combustion behaviour of some biodesulphurized coals assessed by TGA/DTA

Thermal analysis, i.e. TGA/DTA is used to study the changes in the combustion behaviour of microbially treated coals. In view of their high sulphur content and industrial significance three samples are under consideration, i.e. one lignite and two subbituminous from different region in Bulgaria. The differences in burning profiles can be related to structural changes resulted from biological treatments. The overall biological treatment generates these changes probably due to the oxidation process. Concerning organic sulphur biodesulphurization there is no change in any drastic manner of the thermal characteristic parameters. In general, applied biotreatments provoke a complex influence on combustion coal behaviour. From one side a better ignition performance, a minor decrease in higher heating value and diminishing peak temperature of maximum weight loss rate for all biotreated samples are observed. From other side some decrease in the combustibility indicated by an increase in the combustion time and the end of combustion temperature are obvious. Also well determined decrease of self-heating temperature after biotreatments evolves high risk of spontaneous unmanageable coal combustion.

On the utilization of waste vegetable oils (WVO) as agglomerants to recover coal from coal fines cleaning wastes (CFCW)

Coal fines cleaning wastes (CFCW) from two different Spanish coal cleaning plants were agglomerated with waste vegetable oils (WVO) of household origin over a wide range of oil concentration with the aim of recovering high-calorific value/low-ash content coal. The results were evaluated in terms of organic matter recovery (OMR) and ash rejection (AR) from CFCW. In addition to the WVO concentration, the effects of desliming the CFCW and the agglomerates separation method were also studied. In practice, ready to burn coal fines were recovered by this procedure. Moreover, both the risk of spontaneous combustion of coal dumps and the amount of coal wastes to be handled and disposed of can be reduced. Since the feasibility of recovering coal from CFCW by oil agglomeration will depend very much on the cost of oil, the suitability of the WVO to behave as coal agglomerants as well as their low cost are of significance for the commercial viability of the process.

A NEW DIMENSION TO STUDIES OF SPONTANEOUS COMBUSTION OF COAL

Spontaneous combustion of coal is a hazard frequently encountered in coal mining. It has been researched extensively but the actual mechanism by which it occurs is not completely understood. Under suitable conditions, the spontaneous combustion hazard manifests itself in all major aspects of coal mining, namely, underground coal mining, surface mining, stockpiling of coal at the pithead, power stations and ports, during sea-borne transport and stacking of reject material. In underground coal mining, the most difficult situation occurs when spontaneous combustion takes place in the presence of an inherently explosive atmosphere which may promote a local spontaneous combustion incident into an explosion hazard involving the entire mine. Such an incident at the Moura mine in Central Queensland resulted in greater pressure on mine operators for the safe management of spontaneous combustion in their underground coal mines than ever before. As not all coal mines are equally liable to spontaneous combustion due to the different propensities of different coals to self-oxidation, the risk assessment for spontaneous combustion is a primary requirement for the development of a spontaneous combustion management plan for a mine. Once the coal seam has been classified into various categories of spontaneous combustion risk, it is necessary to determine a fire ladder for the coal seam. This should be followed by detailed planning of the mine layout including the mine ventilation system and a spontaneous combustion monitoring program before devising a spontaneous combustion management plan as required by the Coal Mines Underground Regulations 1999. In this paper, a case history is presented which includes the development of a spontaneous combustion management plan for a high-risk coal seam in a greenfield site, from the risk assessment stage to the outbreak stage of a spontaneous combustion incident. It is concluded that the risk assessment, evaluation of the fire ladder, comprehensive monitoring by a tube bundle system and trending of carbon monoxide/oxygen deficiency ratio (Graham's ratio) and CO levels were the main elements in an effective spontaneous combustion control system for the mine.

Coal recovery from fines cleaning wastes by agglomeration with colza oil: a contribution to the environment and energy preservation

The objectives of this work were to recover high-calorific value/low-ash content coals from coal fines cleaning wastes by agglomeration with colza oil and to decrease the risk of spontaneous combustion of the dump where the coal wastes are disposed of. Three Spanish coal fines wastes from different coal cleaning plants were agglomerated with refined colza oil over a wide range of oil concentration. The results were evaluated by the percentages of organic matter recovery and ash rejection as well as the ash content of the recovered coal and the amount of organic matter remaining in the dump after oil agglomeration. It was concluded that the agglomeration of coal fines wastes with colza oil allows the recovery of significant amounts of energy that is currently wasted and reduces the risk of spontaneous combustion of coal dumps as well as the amount of coal fines wastes to be handled and disposed of.

DETERMINATION OF SPONTANEOUS COMBUSTION RISK POTENTIAL OF COLLIERY WASTES FOR THE ENVIRONMENTAL IMPACT ASSESSMENT

Mineral Resources EngineeringVol. 05, No. 03, pp. 229-239 (1996) No AccessDETERMINATION OF SPONTANEOUS COMBUSTION RISK POTENTIAL OF COLLIERY WASTES FOR THE ENVIRONMENTAL IMPACT ASSESSMENTB. UNVERB. UNVERDepartment of Mining Engineering, Hacettepe University, Beytepe, Ankara, 06532, TurkeyFax: +312 235 43 14. Search for more papers by this author https://doi.org/10.1142/S0950609896000170Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail AbstractThousands of tons of coal bearing minestones are obtained each year during underground and open-pit production operations and from coal washery tailings. These wastes can be very detrimental for environment. On the other hand, minestone can be successfully used as a backfill and construction material for roads and embankments. Whenever, the colliery waste is used for civil engineering constructions, it is appropriate to know the characteristics of waste, especially its potential liability to spontaneous combustion. Very serious environmental problems are encountered by means of uncontrolled burning of colliery wastes in tips and lagoons. This paper presents the results of spontaneous combustion risk tests of minestones obtained from nine different locations in England and discusses the precautions to be taken against spontaneous combustion of minestones. Therefore, it would be possible to assess the use of wastes properly for construction purposes by considering the spontaneous risk potential. FiguresReferencesRelatedDetails Recommended Vol. 05, No. 03 Metrics History PDF download

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 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.

Evaluating the risk of spontaneous combustion in coal stockpiles

A mathematical model to predict spontaneous combustion in coal stockpiles is formulated. This model is derived by breaking up the dump into three regions where different effects dominate. The model incorporates a one-dimensional ‘chimney region’, as used by Brooks and Glasser 5, where reaction, heat transfer and flow occur. It is assumed that gas entering the bottom of the chimney is already depleted of oxygen by flow through the rest of the cold coal bed; this depletion is modelled using a residence time distribution approach. Heat transfer (against the direction of flow) is also assumed to take place away from the chimney and this constitutes the third part of the model. The steady-state set of equations describing this system are obtained and solved under some assumptions. It is shown that coal stockpiles may be classified as either safe, unsafe or conditionally safe. It is also shown that there exists a ‘worst depth’. This is defined as the depth, for a given particle size, at which the average temperature in the bed assumes its highest value. The choice of the chimney radius does not drastically effect the results obtained from the model. It is further shown that the important parameters that affect the safety of a coal bed are: the particle size of the coal; the voidage of the bed; and the reaction rate parameters. As these parameters are changed, the average steady-state temperatures in the stockpile are affected, as are the boundaries between the safe, conditionally safe and unsafe regions. The results are presented graphically, and help to provide an understanding of the important factors which decide whether or not coal stockpiles will spontaneously combust.

Sulfur/sodium bentonite mixtures as sulfur fertilizers. 1. The effects of S/Na-bentonite ratios on the rate of dispersion and particle size distribution of elemental sulfur dispersed from laboratory-produced prills

Sulfur/sodium bentonite fertilizer prills were made by blending between 5 and 40% by weight of a swelling sodium bentonite clay with molten sulfur (S) and chilling droplets of the mixtures in oil. The resulting prills were hard and dust free and thus offered a suitable form for elemental sulfur (S°) transportation and application. The prills were stable at normal room temperature and RH. Prill strength was much reduced by prolonged storage at 80% RH. With 15% or more bentonite the bulk resistivity was sufficiently low that no electrostatic charge build-up was likely and consequently there was little risk of spontaneous combustion. Prills containing 10% or more bentonite disintegrated when placed in water and both the rate of dispersion and the fineness of the dispersed S° particles increased bentonite content. Bentonite contents of 15–20% appeared to offer the best combination of rapid prill dispersion, fine dispersed S° particle size, and high S° content.

Completion techniques in deep geothermal drilling

The difficulties encountered during deep drilling ( > 3000 m ) in the Larderello area are caused by: • —highly fractured geological formations which prevent well completion with mud circulation, • —compact formations and, in particular, frequent variations in direction and inclination of bedding, leading to problems in achieving a vertical hole, • —high temperatures and high reservoir pressures and, • —extremely corrosive fluids in the well, and, in some cases, risk of spontaneous combustion. This paper analyses the problems arising during the first geothermal drilling and describes technological developments and experiments aimed at improving drilling techniques and materials. The most important points are: • —casing and cementation at the top of the deep reservoir, to insulate the shallow productive zone, • —control of damage and corrosion in tubular goods, • —adequate fishing techniques and/or operations to remove blockages, • —air drilling in the final phase of the well and, • —instrumentation for controlling and recording well fluid characteristics. Experiments and research on new materials are aimed at solving the serious problems caused by high temperatures and fluid composition. The risk of spontaneous combustion of fluids is also briefly described.