A comprehensive hazard evaluation system for spontaneous combustion of coal in underground mining
Introduction
As the fundamental energy source in China's production industry, coal has occupied a pivotal position in development of the national economy. However, coal fires, induced by spontaneous combustion have greatly threatened the mining industry and have been considered as one of the major disasters in China. Among China's state-owned collieries, 56% of the mines have been jeopardized by spontaneous combustion, and accounts for 90–94% of the total coal mine fires (Li, 1998). Together with huge economic losses and personal casualties, the damage resulting from coal fires have also led to massive environmental contamination (Glenn and Tammy, 2004).Thus, coal fires are an urgent problem to solve.
In recent years, in order to facilitate the prevention and offer solutions against coal fires, the mechanism of spontaneous combustion has been widely and intensively researched from a variety of aspects: volatile particulates, water and ash content, inorganic components, particle size, petrographic composition, etc. (Chandra and Prasad, 1990, Qing, 1993, Bhat Agarwal, 1996, Sujanti and Zhang, 1999, Ward, C.R., 2002) Thus, various methods of investigating the tendencies of spontaneous combustion have been developed (Beamish et al., 2002, Zhou and Wang, 2004). Nevertheless, through analyzing the historical records of coal mine fires, it can be seen that the hazard of spontaneous combustion was not only influenced by the characteristics of coal, but by a multiplicity of factors like underground environment, mining methods, fire prevention (Colaizzi 2004, Zhou et al., 2006) and monitoring systems. Most domestic collieries have attributed the occurrence of fire to the high ignition propensity of coal itself, without taking the initiative in reducing the spontaneous combustion hazard from extrinsic perspectives like improving ventilation or launching fire prevention projects.
To alter the traditional concept, the prediction of coal fire should not be based on the unilateral identification of spontaneous combustion propensity of coal (China State Administration of Work Safety, 2009), but on a comprehensive hazard assessment system, which contains diverse factors and complicated interactions.
Kevin et al. (1988) from South Africa have probed into the hazard of spontaneous combustion of coal stockpiles from both intrinsic and extrinsic aspects, but the theory they applied could hardly be applied to assessing the hazard of coal seams. Singh et al. (2002) from Australia have established a system for quantitatively evaluating the hazard of coal mine fires in local collieries; The United States Bureau of Mines (1994) has researched and developed an application program for comprehensive hazard ratings. However, the geological conditions of Chinese coal mines are relatively intricate, and the mining methods here, including mining technology and mechanical equipment, are largely discrepant in comparison with the West (for example, in China, Top Coal Caving was widely applied, but it was not either in the USA or Australia), so the above mentioned evaluation systems were limited in the characteristics of their local coal mines and could hardly be generalized to the Chinese collieries. In China, some researchers have utilized the neural network model (Wang et al., 2008) and the non-parametric discriminant analysis model (Chen, 2008) to forecast the incubation period of coal fires, but formalizing the models demands numerous learning samples. The judging indicators were also insufficient. Thus; the methods introduced above were not practical and ineffective when applied.
Therefore, it is necessary to carry out a complete and valid evaluation on the hazards of spontaneous combustion. When preparing our research, we collected related data cited from the latest studies on spontaneous combustion research from around the world, and selected those which were applicable to the evaluation of Chinese collieries. Based on the available data, we reconsidered the factors leading to spontaneous combustion, and integrated all the newfound factors into a comprehensive coal fire hazard assessment system which is conducive to both prediction and management. In this paper, we've also applied the model of Analytic Hierarchy Process (AHP) to judge the significance of each factor in influencing the hazard. In order to facilitate the evaluations, a user friendly application software has been developed that assists the evaluators and simultaneously offers reliable recommendations for the prevention of fires. Through practical application tested on 3 collieries, the hazard ratings have been proven to be objective and reasonable.
Section snippets
Specifying evaluating indicators
According to previous studies, coal may naturally burn when the following four factors coincide:
- 1)
Coal with spontaneous combustion tendency;
- 2)
Continuous ventilation condition for transmitting oxygen;
- 3)
Condition for accumulating heat;
- 4)
Exposure time of the coal to air.
The event tree we structured is dependent on the above 4 points coinciding as the necessity for spontaneous combustion. The factors influencing the occurrence of coal fires have been expanded and deployed systematically. Ultimately, 50
The development of spontaneous coal mine fire hazard assessment software
Based on the Microsoft Visual Basic 6.0, we developed an application assisting the hazard evaluation. The application consists of 4 sections — User login, User operation, Evaluating interface and Database. The brief structure is shown in Fig. 3.
The program provides a window for users to input their information, including coal mine's name, surveyor's name and date, which helps the user load and output the historical data easily.
After login, user may select or enter the data according to the
Hazard ratings
There are three domestic collieries for application — Laiyegou Colliery (seam 6–2), Gequan Colliery (seam 9#), Xiandewang Colliery (seam 1# in 9th field), respectively identified with three different heating potentials — extremely flammable, flammable, and nonflammable. Each of them has been recorded with fire history.
Based on the Colliery Spontaneous Combustion Hazard Assessment Program introduced above, we completed the evaluation by imputing the practical data (including coal
Summary and conclusions
The spontaneous combustion of coal is one of the key factors, which results in the instability and low yield during the mining process. In order to plan an effective precaution against coal fires, hazard assessment is an irreplaceable precondition. In this paper, through an integral analysis from diverse perspectives, we have established an advanced system for assessing the hazard of spontaneous coal combustion and subsequently developed an application program which simplifies the evaluating
Acknowledgements
The financial support by National Natural Sciences Foundation of China (Grant No. 50604014), NECT of Ministry of Education (NCET-08-0838), and the Research Fund of the State Key Laboratory of Coal Resources and Mine Safety, CUMT (09KF11) is deeply appreciated.
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