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Development a New Classification for Assessing the Coal Mine Mechanization / Opracowanie nowej klasyfikacji dla oceny mechanizacji w kopalniach węgla

Development a New Classification for Assessing the Coal Mine Mechanization / Opracowanie nowej... Arch. Min. Sci., Vol. 58 (2013), No 1, p. 217­226 Electronic version (in color) of this paper is available: http://mining.archives.pl DOI 10.2478/amsc-2013-0015 HOSSEINI SEYED MEHDI*, MIKAEIL REZA**, ATAEI MOHAMMAD*, REZA KHALOKAKAEI*, MASOUD AKHYANI* DEVELOPMENT A NEW CLASSIFICATION FOR ASSESSING THE COAL MINE MECHANIZATION OPRACOWANIE NOWEJ KLASYFIKACJI DLA OCENY MECHANIZACJI W KOPALNIACH WGLA The coal mine mechanization is important to achieve optimum quality and maximum efficiency of coal production. Mechanization is an objective that can result in significant cost reductions and higher levels of profitability for underground mines. The potential of coal mine mechanization depends on some important factors Such as seam inclination and thickness, geological disturbances, seam floor conditions and roof conditions. These factors should be considered in coal mine mechanization analysis. In this study, the new classification was developed with the respect to the mentioned factors. Using this system the coal seam mechanization index (CSMi) of several types of coal seams was evaluated and classified into five categories; very good, good, medium, low and very low. As a case study, the mechanization of the Takht coal seams in Golestan area of Iran was investigated using this new classification system. The results show a low potential for mechanization in most of the Takht coal seams. Keywords: mechanization, coal seams, Classification system, CSMi Mechanizacja prac w kopalniach wgla jest konieczna dla osignicia maksymalnej wydajnoci produkcji i uzyskania wgla najwyszej jakoci. Mechanizacja jest celem, który skutkowa bdzie znacznym obnieniem kosztów oraz zwikszeniem poziomu rentownoci produkcji w kopalniach podziemnych. Moliwoci mechanizacji w kopalniach uzalenione s od szeregu wanych czynników, takich jak nachylenie i miszo zloa, obecno zaburze struktury geologicznej a take warunki stropowe i spgowe. Czynniki te koniecznie uwzgldni naley w analizach moliwoci mechanizacji pracy kopalni. W pracy tej przedstawiono now klasyfikacj opart o wyej wymienione czynniki. W oparciu o przyjte podejcie, obliczony zostal wskanik mechanizacji dla zloa wgla i nastpnie zastosowany zostal do analiz. Na jego podstawie wyodrbniono pi kategorii zló wglowych w kontekcie moliwoci mechanicznego urabiania: bardzo dobre, dobre, rednie, niskie i bardzo niskie. Jako studium przypadku przedstawiono analiz zloa wglowego Takht w regionie Golestan w Iranie, w oparciu o zaproponowany nowy system klasyfikacji. Wyniki analizy wskazuj, e wikszo zló w regionie Takht stwarza niewielkie moliwoci dla zastosowania mechanizacji. Slowa kluczowe: mechanizacja wydobycia, zloe wglowe, system klasyfikacji, wskanik mechanizacji dla danego zloa * DEPARTMENT OF MINING, SHAHROOD BRANCH, ISLAMIC AZAD UNIVERSITY, SHAHROOD, IRAN ** DEPARTMENT OF MINING AND METALLURGICAL ENGINEERING, URMIA UNIVERSITY OF TECHNOLOGY, URMIA, IRAN 1. Introduction One of the most important tasks in coal mines is to improve efficiency for increasing the production rate of coal besides keeping safety constantly in mind. In order to achieve this aim, mine mechanization is required. Mine mechanization needs high levels of investment and should therefore be studied carefully before final decisions about mechanization are made. For these reasons mining engineers are continuously looking for different ways to mechanize mining procedures, especially the mechanization of underground coal mines that provide a large potential for reduced costs, increased safety and improved profitability. Mechanization and automation are changing the way in which ore deposits are being mined. The industry needs more energy-efficient methods, systems and approaches. For many years, machines have been used to excavate soft minerals in underground mines on a continuous basis. In some cases, this includes soft or weak rocks, surrounding the valuable minerals which are being extracted. Coal is probably the most common example. The methods of working coal seams have gradually evolved and are progressively improved or modified as knowledge and experience are gained and power machines become available. Over the years, a very large number of coal mining methods have been developed to suit seams and local conditions; these may be split broadly into long wall and pillar methods of working. The long wall coal mining method is widely perceived to be a twentieth century development; however, the concept is actually believed to have been developed more than 200 years ago. Its main advance is that earlier operations were, in principle, manual, while since the 1950s, the level of mechanization has increased to the stage that today long wall faces are highly productive units which can be operated by a very small work crew. This method has a simple system layout and provides for continuous production and full potential for mechanization, which can further improve productivity, personnel health and safety. Mechanized long walls rather than other coal mining methods are more expensive to equip and operate, but are in general more productive (Ataei et al., 2009). In this study, the predicting the mechanization of coal seam was investigated by a new classification system. As a case study, the mechanization of Takht coal seams was evaluated using this new classification system. 2. Factors affecting the coal mine mechanization The potential of coal mine mechanization depends on some important factors. The factors affecting the coal mine mechanization can be divided into tow major parts such as characteristics of seam coal and environmental conditions. The characteristics of coal seam are seam inclination, thickness, uniformity and extension. The environmental conditions that affect on coal seam mechanization are seam floor conditions, roof conditions and water at the working face. These factors are given in Figure 1. 2.1. Seam inclination Most long wall mining activities occur in flat ore deposits or nearly flat seams. In general, seams with low a dip (zero or near-zero dip angles) are more amenable for mechanization. With increased seam gradients, the application of mechanization becomes more difficult. Although the best operational conditions are on level seams, in rare cases seams with up to 80 degrees of Seam thickness Characteristics of coal seam Factors affecting the coal mine mechanization Seam inclination Seam Uniformity Seam Extension Roof conditions Environmental condition Floor conditions Water at the working face Fig. 1. Parameters used in coal mine classification system inclination have been worked, although more usually seams up to 35 degree of inclination can be mechanized by power support. The proposed classification for evaluating of seam inclination is given in Table 1. TABLE 1 Proposed classification for determination of seam inclination Seam inclination () 45-70 Very high 30-45 High 15-30 Medium 5-15 Low 0-5 Very low 2.2. Seam thickness The thickness of the seam and its regularity is an important determinant of the level of mechanization that could be applied at a typical coal face. Supports can be lengthened and further increased by some additions. However, great irregularities cannot be accommodated. Cutting low sections may be difficult for the winning machines and washing facilities. Therefore, a good survey of the seam should be made before choosing proper support. The thickness that can be worked, at present, ranges from 0.6 to 5 m with most seams between 1 and 3 m. In seams thicker than 3 m or thinner than 0.6 m, the possibility of mechanization will be reduced. Thicker seams should be worked out in slices or by recovering the caved coal from the back by special arrangements. The proposed classification for evaluating of seam thickness is given in Table 2. TABLE 2 Proposed classification for determination of seam thickness Seam thickness (m) 0.6-1.0 Very narrow 1.0-1.4 narrow 1.4-2.4 medium 2.4-4.5 Thick 4.5-6 Very thick 2.3. Geological disturbances The effect of faulting on the geomechanics of long walls is one of the most difficult issues to predict. In some cases, the presence of faults or jointing can have a dominant effect on the geomechanics of a retreating long wall. If there are complex geological conditions such as faults and seam pinch-outs, the possibility of mechanization will be reduced. The amount of coal seam displacement and the number of faults present over the length of a seam are very important factors that affect the condition of the working face and the decision to mechanize the operation of the seam. In our study, we have defined the displacement index (It), a parameter, to quantify geological disturbances as follows: It = t m (1) Where t is the displacement of a seam by faults (m) and m is the thickness of the seam (m). Table 3 shows the level of seam uniformity with respect to the index of displacement. In this classification, seam uniformity ranges from 0 to 1, where seams with an index It = 0 are completely uniform and seams with a displacement index of more than 3, are considered to be non-uniform. The proposed classification for evaluating of seam uniformity is given in Table 3. TABLE 3 Proposed classification for determination of seam uniformity 2.25-3.0 1.5-2.25 1.0-1.5 0.5-1.0 0-0.5 Seam uniformity Condition (Im) Very low uniform Low uniform Semi uniform High uniform Very high uniform 2.4. Roof conditions Roofs should cave. If a roof does not cave or hangs, it is not suitable for long wall mining because it may fall unexpectedly. Thus, some stowing system should be used. The most suitable roofs cave in as the support advances. However, when a very weak roof crumbles rather than holds, part of the coal seam is left to support it. Both operational experience and research results have demonstrated that roof stability is relative. For an unstable roof, certain techniques are required to control and change the factors contributing to the unstable conditions and to upgrade its stability. For a medium stable roof, a power support is required, properly selected and applied, to maintain roof stability. Often a medium stable roof becomes unstable due to periodic weighing, poor roof conditions or improperly selected power supports. For stable roofs, with the exception of a gradually sagging roof, their stability must be destroyed artificially and systematically in order to avoid large aerial caving. Other quantitative methods are available for evaluating the propensity of roofs to cave in. These methods employ various factors such as litho logical sequences, amount of roof convergence at the gob edge, lack of support over a certain time period before caving, seismic wave velocity, drill core strength, average frequency of bedding plane and rock strength and bed separation resistance. Unrug and Szwilski (1982) made recommendations concerning the principal strata control parameters for the design of long wall faces. Their empirical formula for determining the roof strength index is given as (Unrug & Szwilski, 1982): Qr = 0.016 ´ sc ´ K1 ´ K 2 ´ K 3 ´ m K -1 (2) where Qr is the roof strength index, c the average uniaxial compressive strength of the core (kg/cm2), K1 a factor to account for a decrease in strength from the laboratory to a field specimen, K2 a factor to account for a decrease in strength with creep loading, K3 a factor to account for decrease in strength with an increase in humidity, m the thickness of the immediate roof (cm) and K a swelling coefficient with a value between 1.3-1.5. The various design parameters are based on a roof classification system represented by the roof strength index (Table 4). Table 5 shows the values of different factors for various types of roofs. Finally, the proposed classification for evaluating of roof strength is given in Table 6. TABLE 4 Cave ability classification based on roof strength and time exposure (Unrug & Szwilski, 1982) Roof type Roof strength index (kg/cm2) Description Unstable Low stable Medium stable Stable Very stable 0 Q 18 18 Q 35 35 Q 60 60 Q 130 Q 130 After exposure, roof caves in immediately or after a short delay Roof very difficult to control. Full of cavities, fractures and fissures, caves in easily Caves in easily. From fractured roof with local falls to fairly good roof Good roof with excellent caving properties to hardly any caving Very strong and very stable. Artificial caving is necessary TABLE 5 Values of different factors for different rocks Rock type K1 K2 K3 Sandstone 0.33 0.7 0.6 Mudstone 0.42 0.6 0.4 Siltstone 0.5 0.6 0.4 TABLE 6 Proposed classification for determination of roof strength Roof strength (kg/cm2) 0 Q 18 Unstable 18 Q 35 Low stable 35 Q 60 Medium stable 60 Q 130 Stable Q 130 Very stable 2.5. Floor conditions The floor should be strong enough to resist intrusions. Intrusion of soft floors is troublesome for advancing and also makes the roof conditions difficult to control owing to high convergence. Some coal may be left if the coal is hard. The reaction of floors to any kind of support, installed along or behind long wall faces, significantly affects strata stability. If the design of the support is to be based on an acceptable rate of closure or deformation along a long wall face and its ends, then, in order to ensure support balance and stability, the stratum pressure within the face region should be controlled. This requires: (a) uniform pressure and deformation distribution along the face; (b) a floor bearing capacity in excess of the effective stratum pressure exerted upon it through the supports (Afrouz et al. 1988). Where footwall rocks are weak, support systems may fail by punching into the peripheral rock of ore bodies. The failure mode is analogous to bearing capacity failure of a foundation and may be analyzed as such. The floor rock bearing capacity is direct related with the uniaxial compressive strength of rocks. In general, a higher strength implies a greater bearing capacity and a greater potential for mechanization of the seam. The proposed classification for evaluating of bearing capacity is given in Table 7. TABLE 7 Proposed classification for determination of bearing capacity Bearing capacity (MPa) 0-30 Unstable 30-50 Low stable 50-70 Medium stable 70-90 Stable 90< Very stable 2.6. Water at the working face Water at the working face is detrimental and corrosive to the supports. Under these conditions either the panel should be drained by drilling, or special anticorrosive supports should be chosen. Water is always a handicap and miners hate to work under wet conditions. The proposed classification for evaluating of water at the working face is given in Table 8. TABLE 8 Proposed classification for determination of water at the working face Index 150< Water at the working face (m3/min)* Very aqueous 50-150 aqueous 20-50 Very wet 10-20 wet 0-10 dry * m3 per minute for each 10m of face length 2.7. Extension of Seam The panel should be large enough to use powered supports. It takes 15­20 days to install the equipment, which adds to the cost of the coal; the larger the panel the lower the installation cost per ton of extracted coal. However, very large panels may be expensive in upkeep of the gateways, although this is not an insurmountable problem. The optimum width is found to be 800­1000 m. TABLE 9 Proposed classification for extension of seam Extension of Seam (m) 200-600 Very small 600-1000 small 1000-2000 medium 2000-4000 large 4000< Very large 3. Development a new classification system Until now, no comprehensive classification has been developed for evaluating the coal seam mechanization. The main objective of this paper is to present a new classification system for evaluating the effective factors on coal seam mechanizability using the analytic hierarchy process (AHP). This research considers the coal seam mechanization classification as a decision problem and applies AHP method as a tool for weighting calculations. Finally, a new classification system named ``coal seam mechanization index (CSMi)'' is presented and described. Analytic hierarchy process (AHP) is a multi attribute decision- making (MADM) technique that was first developed in 1980 by Thomas Saaty (Saaty, 1980). It is a tool to combine qualitative and quantitative factors in the selection of a process, and is used for setting priorities in a complex, un-anticipated, multi-criteria problematic situation. Firstly, according to AHP method the pair-wise comparison matrix was built by using Saaty's 1-9 scale. This pair-wise comparison is shown here: é êc ê1 êc2 ê êc3 êc4 ê êc5 êc ê6 êc7 ë c1 1 1/ 2 1/ 2 1/ 2 1/ 4 1/ 5 1/ 3 c2 2 1 1 1 1/ 2 1/ 3 1/ 2 c3 2 1 1 1 1/ 3 1/ 4 1/ 2 c4 2 1 1 1 1/ 3 1/ 3 1/ 2 c5 4 2 3 3 1 1/ 2 2 c6 5 3 4 3 2 1 3 c7 ù 3 ú ú 2 ú ú 2 ú 2 ú ú 1 /2 ú 1/3 ú ú 1 ú û c1: Seam inclination c2: Seam uniformity Condition c3: Seam thickness c4: Roof strength c5: Bearing capacity c6: Water at the working face c7: Seam Extension Finally, the calculated weights of major parameters are shown in Table 10. TABLE 10 The calculated weights of major parameters Parameters Weight Seam inclination Seam thickness Roof strength Seam uniformity Condition Seam Extension Bearing capacity Water at the working face In the new classification system, the coal seam was classified into five categories: excellent, good, fair, poor and very poor. In the new classification system to rate the various values of each parameter, the most weights have been rated for the excellent mode. Rates of good, fair, poor and very poor determined, respectively, 70%, 50%, 25% and 10% of excellent mode. By order of above rating, the classification system becomes non-linear (Hoseinie et al., 2008, 2009; Mikaeil et al., 2011). Considering relative importance of the various parameters utilized for assessment of coal seam mechanization index, it has been assumed that the total rate is 100 as a maximum, which represents the best conditions of mechanization. The coal seam mechanization classification and is given in Table 11. Moreover, one user can classify and qualitatively predict the mechanizability of coal seam with use of Table 12. TABLE 11 Coal seam mechanization classification Seam inclination Score Seam thickness 45-70 30-45 15-30 5-15 0-5 2.9 7.25 14.5 20.3 29 0.6-1.0 1.0-1.4 1.4-2.4 2.4-4.5 4.5-6 Very narrow narrow medium Thick Very thick Score 1.8 4.5 9 12.6 18 2.25-3.0 1.5-2.25 1.0-1.5 0.5-1.0 0-0.5 Seam uniformity condition Very low uniform Low uniform Semi uniform High uniform Very high uniform Score 1.6 4 8 11.2 16 >130 0-18 18-35 35-60 60-130 Roof strength Unstable Low stable Medium stable Stable Very stable Score 1.7 4.25 8.5 11.9 17 0-30 30-50 50-70 70-90 90< Bearing capacity Unstable Low stable Medium stable Stable Very stable Score 0.6 1.5 3 4.2 6 150< 50-150 20-50 10-20 0-10 Water at the working face Aqueous wet dry Score 0.4 1 2 2.8 4 200-600 600-1000 1000-2000 2000-4000 4000< Extension of seam Very small small medium large Very large Score 1 2.5 5 7 10 TABLE 12 Prediction of coal seam mechanization using CSMi CSMi Description Mechanizability 10-20 Very low Very poor 20-40 Low Poor 40-60 Medium Medium 60-80 High Good 80-100 Very high Very good 4. Case study The Eastern Alborz coal basin is located in northern Iran and presently includes all the carboniferous sediments contained within the bounderieas formed by the Firoozkooh road and the Bojnord-Esfarayen road (Doulati Ardejani et al., 2008). Our exploration studies also include the carboniferous sediments in the margin of the central desert in Iran such as the ChahshirinJam and Larestan and on the east side our study area continued to the Sarakhs. The Takht coal mine is one of a number of mines in the Eastern Alborz coal basin, situated to the south east of Minoodasht city in Golestan Province (Iran). In this study, the potential for mechanization of the Takht coal seams were investigated by using the new classification system. Table 13 shows the result of this study of the potential for mechanization of these coal seams. The results show that the 4 seams of total studied seam was high potential and 2 seams was medium potential for mechanization of the Takht coal seams. Totally, it is obvious that the 67 percent of total Takht seams have a good condition for mechanization. TABLE 13 Potential for Mechanization of the Takht coal seams Water at the working face (m3/min) Seam Inclination (°) Seam uniformity Seam Thickness (m) Extension of seam (m) Roof Strength (kg/cm2) Bearing capacity (MPa) Potential for Mechanization Score Qi Seam K8 K10 K11 K17 K19 K20 Medium High Medium High High High 5. Conclusions The most important objectives of mechanization are follows: reduced costs; faster development; faster mining; safer mining; concentrating production at fewer locations; achieving higher production rates per shift; mining with smaller underground crews; smaller capital expenditure per extracted ton of coal; work under protectively supported roofs; development of more productive crews. Coal has always been considered an important source of energy and despite short-term fluctuations; its long-term total demand in the world shows an upward trend. Reducing costs, achieving higher production rates per shift and increasing safety levels are the most important problems in Iranian coal mines. Therefore mine mechanization is required. Mine mechanization needs large amounts of investments and should therefore be studied carefully before final decisions on the implementation of mechanization. In this study, the most important parameters affecting the feasibility of using mechanized mining of coal seams have been presented in terms of seam gradient and thickness, geological disturbances, seam floor conditions, roof formation and water at the working face. In our study, a new classification system has been developed based on analytic hierarchy process (AHP) technique and by using the seam gradient and thickness, geological disturbances, seam floor conditions, roof formation and water at the working face. The potential for coal seam mechanization can be evaluated by using this classification system with use of a new index named coal seam mechanization index (CSMi). Potential mechanization of the Takht coal mines in Iran was investigated as a case study. The results showed that the 67 percent of total studied seam was high potential and 33 percent was medium potential for mechanization of the Takht coal seams. Acknowledgment The authors would like to thank the Islamic Azad University, Shahrood Branch, Shahrood, Iran for providing the facilities in order to perform an original research. 226 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Mining Sciences de Gruyter

Development a New Classification for Assessing the Coal Mine Mechanization / Opracowanie nowej klasyfikacji dla oceny mechanizacji w kopalniach węgla

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10.2478/amsc-2013-0015
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Abstract

Arch. Min. Sci., Vol. 58 (2013), No 1, p. 217­226 Electronic version (in color) of this paper is available: http://mining.archives.pl DOI 10.2478/amsc-2013-0015 HOSSEINI SEYED MEHDI*, MIKAEIL REZA**, ATAEI MOHAMMAD*, REZA KHALOKAKAEI*, MASOUD AKHYANI* DEVELOPMENT A NEW CLASSIFICATION FOR ASSESSING THE COAL MINE MECHANIZATION OPRACOWANIE NOWEJ KLASYFIKACJI DLA OCENY MECHANIZACJI W KOPALNIACH WGLA The coal mine mechanization is important to achieve optimum quality and maximum efficiency of coal production. Mechanization is an objective that can result in significant cost reductions and higher levels of profitability for underground mines. The potential of coal mine mechanization depends on some important factors Such as seam inclination and thickness, geological disturbances, seam floor conditions and roof conditions. These factors should be considered in coal mine mechanization analysis. In this study, the new classification was developed with the respect to the mentioned factors. Using this system the coal seam mechanization index (CSMi) of several types of coal seams was evaluated and classified into five categories; very good, good, medium, low and very low. As a case study, the mechanization of the Takht coal seams in Golestan area of Iran was investigated using this new classification system. The results show a low potential for mechanization in most of the Takht coal seams. Keywords: mechanization, coal seams, Classification system, CSMi Mechanizacja prac w kopalniach wgla jest konieczna dla osignicia maksymalnej wydajnoci produkcji i uzyskania wgla najwyszej jakoci. Mechanizacja jest celem, który skutkowa bdzie znacznym obnieniem kosztów oraz zwikszeniem poziomu rentownoci produkcji w kopalniach podziemnych. Moliwoci mechanizacji w kopalniach uzalenione s od szeregu wanych czynników, takich jak nachylenie i miszo zloa, obecno zaburze struktury geologicznej a take warunki stropowe i spgowe. Czynniki te koniecznie uwzgldni naley w analizach moliwoci mechanizacji pracy kopalni. W pracy tej przedstawiono now klasyfikacj opart o wyej wymienione czynniki. W oparciu o przyjte podejcie, obliczony zostal wskanik mechanizacji dla zloa wgla i nastpnie zastosowany zostal do analiz. Na jego podstawie wyodrbniono pi kategorii zló wglowych w kontekcie moliwoci mechanicznego urabiania: bardzo dobre, dobre, rednie, niskie i bardzo niskie. Jako studium przypadku przedstawiono analiz zloa wglowego Takht w regionie Golestan w Iranie, w oparciu o zaproponowany nowy system klasyfikacji. Wyniki analizy wskazuj, e wikszo zló w regionie Takht stwarza niewielkie moliwoci dla zastosowania mechanizacji. Slowa kluczowe: mechanizacja wydobycia, zloe wglowe, system klasyfikacji, wskanik mechanizacji dla danego zloa * DEPARTMENT OF MINING, SHAHROOD BRANCH, ISLAMIC AZAD UNIVERSITY, SHAHROOD, IRAN ** DEPARTMENT OF MINING AND METALLURGICAL ENGINEERING, URMIA UNIVERSITY OF TECHNOLOGY, URMIA, IRAN 1. Introduction One of the most important tasks in coal mines is to improve efficiency for increasing the production rate of coal besides keeping safety constantly in mind. In order to achieve this aim, mine mechanization is required. Mine mechanization needs high levels of investment and should therefore be studied carefully before final decisions about mechanization are made. For these reasons mining engineers are continuously looking for different ways to mechanize mining procedures, especially the mechanization of underground coal mines that provide a large potential for reduced costs, increased safety and improved profitability. Mechanization and automation are changing the way in which ore deposits are being mined. The industry needs more energy-efficient methods, systems and approaches. For many years, machines have been used to excavate soft minerals in underground mines on a continuous basis. In some cases, this includes soft or weak rocks, surrounding the valuable minerals which are being extracted. Coal is probably the most common example. The methods of working coal seams have gradually evolved and are progressively improved or modified as knowledge and experience are gained and power machines become available. Over the years, a very large number of coal mining methods have been developed to suit seams and local conditions; these may be split broadly into long wall and pillar methods of working. The long wall coal mining method is widely perceived to be a twentieth century development; however, the concept is actually believed to have been developed more than 200 years ago. Its main advance is that earlier operations were, in principle, manual, while since the 1950s, the level of mechanization has increased to the stage that today long wall faces are highly productive units which can be operated by a very small work crew. This method has a simple system layout and provides for continuous production and full potential for mechanization, which can further improve productivity, personnel health and safety. Mechanized long walls rather than other coal mining methods are more expensive to equip and operate, but are in general more productive (Ataei et al., 2009). In this study, the predicting the mechanization of coal seam was investigated by a new classification system. As a case study, the mechanization of Takht coal seams was evaluated using this new classification system. 2. Factors affecting the coal mine mechanization The potential of coal mine mechanization depends on some important factors. The factors affecting the coal mine mechanization can be divided into tow major parts such as characteristics of seam coal and environmental conditions. The characteristics of coal seam are seam inclination, thickness, uniformity and extension. The environmental conditions that affect on coal seam mechanization are seam floor conditions, roof conditions and water at the working face. These factors are given in Figure 1. 2.1. Seam inclination Most long wall mining activities occur in flat ore deposits or nearly flat seams. In general, seams with low a dip (zero or near-zero dip angles) are more amenable for mechanization. With increased seam gradients, the application of mechanization becomes more difficult. Although the best operational conditions are on level seams, in rare cases seams with up to 80 degrees of Seam thickness Characteristics of coal seam Factors affecting the coal mine mechanization Seam inclination Seam Uniformity Seam Extension Roof conditions Environmental condition Floor conditions Water at the working face Fig. 1. Parameters used in coal mine classification system inclination have been worked, although more usually seams up to 35 degree of inclination can be mechanized by power support. The proposed classification for evaluating of seam inclination is given in Table 1. TABLE 1 Proposed classification for determination of seam inclination Seam inclination () 45-70 Very high 30-45 High 15-30 Medium 5-15 Low 0-5 Very low 2.2. Seam thickness The thickness of the seam and its regularity is an important determinant of the level of mechanization that could be applied at a typical coal face. Supports can be lengthened and further increased by some additions. However, great irregularities cannot be accommodated. Cutting low sections may be difficult for the winning machines and washing facilities. Therefore, a good survey of the seam should be made before choosing proper support. The thickness that can be worked, at present, ranges from 0.6 to 5 m with most seams between 1 and 3 m. In seams thicker than 3 m or thinner than 0.6 m, the possibility of mechanization will be reduced. Thicker seams should be worked out in slices or by recovering the caved coal from the back by special arrangements. The proposed classification for evaluating of seam thickness is given in Table 2. TABLE 2 Proposed classification for determination of seam thickness Seam thickness (m) 0.6-1.0 Very narrow 1.0-1.4 narrow 1.4-2.4 medium 2.4-4.5 Thick 4.5-6 Very thick 2.3. Geological disturbances The effect of faulting on the geomechanics of long walls is one of the most difficult issues to predict. In some cases, the presence of faults or jointing can have a dominant effect on the geomechanics of a retreating long wall. If there are complex geological conditions such as faults and seam pinch-outs, the possibility of mechanization will be reduced. The amount of coal seam displacement and the number of faults present over the length of a seam are very important factors that affect the condition of the working face and the decision to mechanize the operation of the seam. In our study, we have defined the displacement index (It), a parameter, to quantify geological disturbances as follows: It = t m (1) Where t is the displacement of a seam by faults (m) and m is the thickness of the seam (m). Table 3 shows the level of seam uniformity with respect to the index of displacement. In this classification, seam uniformity ranges from 0 to 1, where seams with an index It = 0 are completely uniform and seams with a displacement index of more than 3, are considered to be non-uniform. The proposed classification for evaluating of seam uniformity is given in Table 3. TABLE 3 Proposed classification for determination of seam uniformity 2.25-3.0 1.5-2.25 1.0-1.5 0.5-1.0 0-0.5 Seam uniformity Condition (Im) Very low uniform Low uniform Semi uniform High uniform Very high uniform 2.4. Roof conditions Roofs should cave. If a roof does not cave or hangs, it is not suitable for long wall mining because it may fall unexpectedly. Thus, some stowing system should be used. The most suitable roofs cave in as the support advances. However, when a very weak roof crumbles rather than holds, part of the coal seam is left to support it. Both operational experience and research results have demonstrated that roof stability is relative. For an unstable roof, certain techniques are required to control and change the factors contributing to the unstable conditions and to upgrade its stability. For a medium stable roof, a power support is required, properly selected and applied, to maintain roof stability. Often a medium stable roof becomes unstable due to periodic weighing, poor roof conditions or improperly selected power supports. For stable roofs, with the exception of a gradually sagging roof, their stability must be destroyed artificially and systematically in order to avoid large aerial caving. Other quantitative methods are available for evaluating the propensity of roofs to cave in. These methods employ various factors such as litho logical sequences, amount of roof convergence at the gob edge, lack of support over a certain time period before caving, seismic wave velocity, drill core strength, average frequency of bedding plane and rock strength and bed separation resistance. Unrug and Szwilski (1982) made recommendations concerning the principal strata control parameters for the design of long wall faces. Their empirical formula for determining the roof strength index is given as (Unrug & Szwilski, 1982): Qr = 0.016 ´ sc ´ K1 ´ K 2 ´ K 3 ´ m K -1 (2) where Qr is the roof strength index, c the average uniaxial compressive strength of the core (kg/cm2), K1 a factor to account for a decrease in strength from the laboratory to a field specimen, K2 a factor to account for a decrease in strength with creep loading, K3 a factor to account for decrease in strength with an increase in humidity, m the thickness of the immediate roof (cm) and K a swelling coefficient with a value between 1.3-1.5. The various design parameters are based on a roof classification system represented by the roof strength index (Table 4). Table 5 shows the values of different factors for various types of roofs. Finally, the proposed classification for evaluating of roof strength is given in Table 6. TABLE 4 Cave ability classification based on roof strength and time exposure (Unrug & Szwilski, 1982) Roof type Roof strength index (kg/cm2) Description Unstable Low stable Medium stable Stable Very stable 0 Q 18 18 Q 35 35 Q 60 60 Q 130 Q 130 After exposure, roof caves in immediately or after a short delay Roof very difficult to control. Full of cavities, fractures and fissures, caves in easily Caves in easily. From fractured roof with local falls to fairly good roof Good roof with excellent caving properties to hardly any caving Very strong and very stable. Artificial caving is necessary TABLE 5 Values of different factors for different rocks Rock type K1 K2 K3 Sandstone 0.33 0.7 0.6 Mudstone 0.42 0.6 0.4 Siltstone 0.5 0.6 0.4 TABLE 6 Proposed classification for determination of roof strength Roof strength (kg/cm2) 0 Q 18 Unstable 18 Q 35 Low stable 35 Q 60 Medium stable 60 Q 130 Stable Q 130 Very stable 2.5. Floor conditions The floor should be strong enough to resist intrusions. Intrusion of soft floors is troublesome for advancing and also makes the roof conditions difficult to control owing to high convergence. Some coal may be left if the coal is hard. The reaction of floors to any kind of support, installed along or behind long wall faces, significantly affects strata stability. If the design of the support is to be based on an acceptable rate of closure or deformation along a long wall face and its ends, then, in order to ensure support balance and stability, the stratum pressure within the face region should be controlled. This requires: (a) uniform pressure and deformation distribution along the face; (b) a floor bearing capacity in excess of the effective stratum pressure exerted upon it through the supports (Afrouz et al. 1988). Where footwall rocks are weak, support systems may fail by punching into the peripheral rock of ore bodies. The failure mode is analogous to bearing capacity failure of a foundation and may be analyzed as such. The floor rock bearing capacity is direct related with the uniaxial compressive strength of rocks. In general, a higher strength implies a greater bearing capacity and a greater potential for mechanization of the seam. The proposed classification for evaluating of bearing capacity is given in Table 7. TABLE 7 Proposed classification for determination of bearing capacity Bearing capacity (MPa) 0-30 Unstable 30-50 Low stable 50-70 Medium stable 70-90 Stable 90< Very stable 2.6. Water at the working face Water at the working face is detrimental and corrosive to the supports. Under these conditions either the panel should be drained by drilling, or special anticorrosive supports should be chosen. Water is always a handicap and miners hate to work under wet conditions. The proposed classification for evaluating of water at the working face is given in Table 8. TABLE 8 Proposed classification for determination of water at the working face Index 150< Water at the working face (m3/min)* Very aqueous 50-150 aqueous 20-50 Very wet 10-20 wet 0-10 dry * m3 per minute for each 10m of face length 2.7. Extension of Seam The panel should be large enough to use powered supports. It takes 15­20 days to install the equipment, which adds to the cost of the coal; the larger the panel the lower the installation cost per ton of extracted coal. However, very large panels may be expensive in upkeep of the gateways, although this is not an insurmountable problem. The optimum width is found to be 800­1000 m. TABLE 9 Proposed classification for extension of seam Extension of Seam (m) 200-600 Very small 600-1000 small 1000-2000 medium 2000-4000 large 4000< Very large 3. Development a new classification system Until now, no comprehensive classification has been developed for evaluating the coal seam mechanization. The main objective of this paper is to present a new classification system for evaluating the effective factors on coal seam mechanizability using the analytic hierarchy process (AHP). This research considers the coal seam mechanization classification as a decision problem and applies AHP method as a tool for weighting calculations. Finally, a new classification system named ``coal seam mechanization index (CSMi)'' is presented and described. Analytic hierarchy process (AHP) is a multi attribute decision- making (MADM) technique that was first developed in 1980 by Thomas Saaty (Saaty, 1980). It is a tool to combine qualitative and quantitative factors in the selection of a process, and is used for setting priorities in a complex, un-anticipated, multi-criteria problematic situation. Firstly, according to AHP method the pair-wise comparison matrix was built by using Saaty's 1-9 scale. This pair-wise comparison is shown here: é êc ê1 êc2 ê êc3 êc4 ê êc5 êc ê6 êc7 ë c1 1 1/ 2 1/ 2 1/ 2 1/ 4 1/ 5 1/ 3 c2 2 1 1 1 1/ 2 1/ 3 1/ 2 c3 2 1 1 1 1/ 3 1/ 4 1/ 2 c4 2 1 1 1 1/ 3 1/ 3 1/ 2 c5 4 2 3 3 1 1/ 2 2 c6 5 3 4 3 2 1 3 c7 ù 3 ú ú 2 ú ú 2 ú 2 ú ú 1 /2 ú 1/3 ú ú 1 ú û c1: Seam inclination c2: Seam uniformity Condition c3: Seam thickness c4: Roof strength c5: Bearing capacity c6: Water at the working face c7: Seam Extension Finally, the calculated weights of major parameters are shown in Table 10. TABLE 10 The calculated weights of major parameters Parameters Weight Seam inclination Seam thickness Roof strength Seam uniformity Condition Seam Extension Bearing capacity Water at the working face In the new classification system, the coal seam was classified into five categories: excellent, good, fair, poor and very poor. In the new classification system to rate the various values of each parameter, the most weights have been rated for the excellent mode. Rates of good, fair, poor and very poor determined, respectively, 70%, 50%, 25% and 10% of excellent mode. By order of above rating, the classification system becomes non-linear (Hoseinie et al., 2008, 2009; Mikaeil et al., 2011). Considering relative importance of the various parameters utilized for assessment of coal seam mechanization index, it has been assumed that the total rate is 100 as a maximum, which represents the best conditions of mechanization. The coal seam mechanization classification and is given in Table 11. Moreover, one user can classify and qualitatively predict the mechanizability of coal seam with use of Table 12. TABLE 11 Coal seam mechanization classification Seam inclination Score Seam thickness 45-70 30-45 15-30 5-15 0-5 2.9 7.25 14.5 20.3 29 0.6-1.0 1.0-1.4 1.4-2.4 2.4-4.5 4.5-6 Very narrow narrow medium Thick Very thick Score 1.8 4.5 9 12.6 18 2.25-3.0 1.5-2.25 1.0-1.5 0.5-1.0 0-0.5 Seam uniformity condition Very low uniform Low uniform Semi uniform High uniform Very high uniform Score 1.6 4 8 11.2 16 >130 0-18 18-35 35-60 60-130 Roof strength Unstable Low stable Medium stable Stable Very stable Score 1.7 4.25 8.5 11.9 17 0-30 30-50 50-70 70-90 90< Bearing capacity Unstable Low stable Medium stable Stable Very stable Score 0.6 1.5 3 4.2 6 150< 50-150 20-50 10-20 0-10 Water at the working face Aqueous wet dry Score 0.4 1 2 2.8 4 200-600 600-1000 1000-2000 2000-4000 4000< Extension of seam Very small small medium large Very large Score 1 2.5 5 7 10 TABLE 12 Prediction of coal seam mechanization using CSMi CSMi Description Mechanizability 10-20 Very low Very poor 20-40 Low Poor 40-60 Medium Medium 60-80 High Good 80-100 Very high Very good 4. Case study The Eastern Alborz coal basin is located in northern Iran and presently includes all the carboniferous sediments contained within the bounderieas formed by the Firoozkooh road and the Bojnord-Esfarayen road (Doulati Ardejani et al., 2008). Our exploration studies also include the carboniferous sediments in the margin of the central desert in Iran such as the ChahshirinJam and Larestan and on the east side our study area continued to the Sarakhs. The Takht coal mine is one of a number of mines in the Eastern Alborz coal basin, situated to the south east of Minoodasht city in Golestan Province (Iran). In this study, the potential for mechanization of the Takht coal seams were investigated by using the new classification system. Table 13 shows the result of this study of the potential for mechanization of these coal seams. The results show that the 4 seams of total studied seam was high potential and 2 seams was medium potential for mechanization of the Takht coal seams. Totally, it is obvious that the 67 percent of total Takht seams have a good condition for mechanization. TABLE 13 Potential for Mechanization of the Takht coal seams Water at the working face (m3/min) Seam Inclination (°) Seam uniformity Seam Thickness (m) Extension of seam (m) Roof Strength (kg/cm2) Bearing capacity (MPa) Potential for Mechanization Score Qi Seam K8 K10 K11 K17 K19 K20 Medium High Medium High High High 5. Conclusions The most important objectives of mechanization are follows: reduced costs; faster development; faster mining; safer mining; concentrating production at fewer locations; achieving higher production rates per shift; mining with smaller underground crews; smaller capital expenditure per extracted ton of coal; work under protectively supported roofs; development of more productive crews. Coal has always been considered an important source of energy and despite short-term fluctuations; its long-term total demand in the world shows an upward trend. Reducing costs, achieving higher production rates per shift and increasing safety levels are the most important problems in Iranian coal mines. Therefore mine mechanization is required. Mine mechanization needs large amounts of investments and should therefore be studied carefully before final decisions on the implementation of mechanization. In this study, the most important parameters affecting the feasibility of using mechanized mining of coal seams have been presented in terms of seam gradient and thickness, geological disturbances, seam floor conditions, roof formation and water at the working face. In our study, a new classification system has been developed based on analytic hierarchy process (AHP) technique and by using the seam gradient and thickness, geological disturbances, seam floor conditions, roof formation and water at the working face. The potential for coal seam mechanization can be evaluated by using this classification system with use of a new index named coal seam mechanization index (CSMi). Potential mechanization of the Takht coal mines in Iran was investigated as a case study. The results showed that the 67 percent of total studied seam was high potential and 33 percent was medium potential for mechanization of the Takht coal seams. Acknowledgment The authors would like to thank the Islamic Azad University, Shahrood Branch, Shahrood, Iran for providing the facilities in order to perform an original research. 226

Journal

Archives of Mining Sciencesde Gruyter

Published: Mar 1, 2013

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