IR@CIMFR - Central Institute of Mining and Fuel Research (CSIR)
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Time-constrained demolition of a concrete cofferdam using controlled blasting
No full textA concrete cofferdam of a hydropower project in India had to be demolished within a limited time period due to impoundment of river water. The cofferdam was trapezoidal at bottom and middle, rectangular at the top and abutted to one of the spillway piers. Two more spillway piers, spillway gates and a dam were very close to it. The length and height of cofferdam were 62 m and 24 m, respectively. For demolition of cofferdam, a new controlled blasting technique was developed after conducting test blasts at different locations. Two test blasts with varying blast designs and charging patterns were conducted at the farthest end of cofferdam which was free from other structures. Two more test blasts were conducted near the abutted portion with a very light explosive charge per hole fired in delayed sequence using half-second electric detonators. Results of the test blasts, particularly ground vibrations, throw of blasted materials and breakage patterns were analysed critically. Based on the results, a cautious blasting zone was determined near the abutted portion and controlled blasting patterns were designed. The formation of a zone of disturbance from cautious blasts at the abutted end for every concrete lift significantly reduced the magnitudes of vibration waves for successive blasting operations in remaining portion of that lift. The use of half-second delay detonators helped in segregating the vibration waves from the holes fired in different delays. The demolition work completed safely within the time limit using cautious blasting technique and systematic sequencing of blasts
Air quality modeling for impact evaluation of a mica, feldspar, and quartz mine in Nellore district, Andhra Pradesh, India
No full textThe dust emission from the mining area is the primary source of air pollution for the surrounding environment. This paper
deals with the study of baseline air quality assessment and air pollution modeling exercise for a mica, feldspar, and quartz
mine to predict the maximum dust concentration from the mine with and without control measures. Baseline PM10, PM2.5,
SO2, and NO2 levels in the bufer zone of the planned mine site were found to be 53.1–79.5, 20.2–43.2, 16.6–31.2, and
21.2–50.1 mg m−3, respectively, and these values were lesser than the corresponding permissible limit of 100, 60, 80, and
80 µg m−3. The respective predicted PM10 and PM2.5 levels will be 73.9–97.1 and 31.9–44.2 mg m−3 without control measures, and 73.5–82.5 and 31.8–43.8 µg m−3 with control measures during operation of the mine. It is estimated that PM10and PM2.5 will remain below the permissible limit in the buffer zone of the mine. The paper suggests effective air pollution control measures, including a description of the developed smart dry fog dust suppression system and wirelessly controlled sprinkling system for applications at various dust emitting sources in the mining area
Assessment of Rockfall Hazard and Stabilization of Rock Slope Surface at the World Heritage Ajanta Cave
No full textThe assessment of rock fall hazard of a
natural rock slope surface with ancient rock cave
monuments of historic importance at World-Heritage
site of Ajanta in the state of Maharashtra in India,
embedded in basaltic rock formation is carried out and
presented. In past the site has witnessed many small
and large scale rock falls in the form of boulders which
could cause the loss to the ancient rock caves of
historic importance as well as en-dangering the
visitor’s safety. The main cause of the rock fall is
dislocation of the boulders from the natural rock
surface slopes due to heavy rainfall as well as due to
erosion, rock weathering, trees roots widening etc. In
the present study, the rock slope surface and dislocated
boulders vulnerability to failure risk is carried out with
the Rockfall Hazard Rating System (RHRS) in tandem
with other empirical approaches available for rock
mass classification. The study using rockfall hazard
rating system requires tedious field-work due to the
involvement of a large number of parameters and
long-stretch of the site under question. The detailed
field study is carried out for the evaluation of various
parameters involved in the RHRS as well as that of
various empirical approaches applied. In the case of
the cumulative RHRS score is more than 500 which implies that the slope surface or critical boulder site is
unstable, prone to failure and need immediate attention for remedial measures. Accordingly, stabilization
measures are planned on the priority basis
Impact of Degassing Time and Temperature on the Estimation of Pore Attributes in Shale
No full textThe influence of degassing time and temperature on low-pressure gas adsorption (LPGA) behavior of shales was examined in this study. Two organic-rich shales of contrasting maturity, reactivity and organic matter type, were crushed to <1 mm and <212 μm grain-sizes and degassed at 110, 200, and 300 °C for 3 and 12 h, respectively. Our results indicate that degassing duration has a minimal influence on pore-character interpretations from LPGA experiments, while the degassing temperature shows a strong influence on the pore attributes. For both shales, reliable porosity estimates were obtained when the samples were degassed at 110 °C. When the degassing temperature was increased to 200 and further to 300 °C, distinct changes in adsorption isotherms and other pore structural features were observed. For the mesoporous low-mature shale (collected from a lignite mine) when the degassing temperature was kept at 200 °C, a macroporous character was induced with a manifold increase in pore diameter. Results from thermogravimetry and Rock-Eval indicate abundance of reactive kerogen, which undergoes alteration when degassed at higher temperatures. When the degassing temperature was kept at 300 °C, the organic matter underwent further alteration and showed an isotherm similar to the shales degassed at 110 °C. Similarly, for the oil-window mature shale sample, a transition towards macroporous structure was observed when the sample was degassed at 200 and 300 °C, compared to a mesoporous structure observed when degassed at 110 °C. The results from fractal dimensions also support the above inferences, indicating the presence of simpler structures at higher degassing temperatures. Reduction in pore volume (110–200 °C) and its further rise (200–300 °C) are also evident in the micropore domain, more distinctly in the oil window mature shale. Our results strongly indicate that degassing temperature should be kept at around 110 °C for reliable shale pore character estimation
Development of empirical model for strength estimation of irregular-shaped-heightened-rib/snook for mechanised depillaring
No full textIssues with conventional depillaring techniques resulted in unscientific development of a number of coal seams into rectangular/square shaped pillars, mainly, located at shallow depths in different coalfields of India. Continuous miner based mechanised depillaring (MD) has been introduced to extract these coal pillars which is the main stage of production. The practise of leaving a proper sized rib/snook is a legal requirement as it decides the efficiency and safety of the MD operation. However, MD of square/rectangular shaped pillars created irregular-shaped-heightened-rib/snook. Conventional empirical formula is not capable to estimate strength of such ribs/snooks. These ribs/snooks should be of sufficient size to protect the adjacent slicing operation and junction as well as it should fail in a controlled manner when shifted inside the goaf. Field studies conducted at 39 panels of 7 different mines found a number of factors affecting the design of rib/snook. Proper assessment of performance of different sizes and shapes of ribs/snooks in field is difficult due to the complex and challenging underground mining environment of depillaring. These challenges prohibit a detailed study to be carried out in field. Therefore, parametric study on calibrated numerical model is conducted to estimate the strength of rib/snook with variation in sizes and heights of rib/snook and depth of cover. Further, an empirical relationship is developed to estimate the strength of rib/snook based on multivariate regression analysis. The values of strength estimated by the developed relationship is found to be least when compared with the popular pillar strength formulations due to effect of pillar/rib/snook spalling observed during field investigation with increase in depth of working. Results of field and simulation studies are presented and discussed in this paper for the design of irregular-shaped-heightened-rib/snook
Co-gasification of High Ash Coal–Biomass Blends in a Fluidized Bed Gasifier: Experimental Study and Computational Intelligence-Based Modeling
No full textCo-gasification (COG) is a clean-coal technology that uses a binary blend of coal and biomass for generating the product gas; it is environment-friendly since it emits lesser quantities of pollutants compared to the coal gasification process. Although coals found in many countries contain high percentages of ash, co-gasification studies involving such coals, and the process modeling thereof, are rare. Accordingly, this study presents results of the co-gasification experiments conducted in a fluidized-bed gasifier (FBG) pilot plant using as a feed the blends of high ash Indian coals with three biomasses, namely, rice husk, press mud, and sawdust. Since the underlying physicochemical phenomena are complex and nonlinear, modeling of the COG process has been performed using three computational intelligence (CI)-based methods namely, genetic programming, artificial neural networks, and support vector regression. Each of these formalisms was employed separately to develop models predicting four COG performance variables, namely, total gas yield, carbon conversion efficiency, heating value of product gas, and cold gas efficiency. All the CI-based models exhibit an excellent prediction accuracy and generalization performance. The co-gasification experiments and their modeling presented here for a pilot-plant FBG can be gainfully utilized in the efficient design and operation of the corresponding commercial scale co-gasifiers utilizing high ash coals
A methodology for designing cutting drum of surface miner to achieve production of desired chip size
No full textThe size of coal chips, produced during coal cutting operations, is of prime importance from the viewpoint of feed size desired by power plants. Proper chip size in cutting can eliminate primary crushing and in-turn save energy. Achieving a designated size of chip is intimately linked with the drum design inter alia the wrap angle, line spacing of picks and pick size. Operating parameters namely cutting speed and drum speed also influence the output. Considering the increased need to produce a sized product for cost-effective mining, a design methodology was developed to achieve a required chip size for surface miners with a middle drum configuration. Various pick, drum and operational parameters were taken into account for the development of drum design, namely drum width, drum diameter, pick size, clearance angle, rake angle, cutting angle, lacing pattern, angle of wrap, depth of cut, indented depth of cut and pick spacing. Limiting factors for drum design such as the number of picks, pick temperature, strength of pick, depth of cut and dust generation were discussed. A new drum configuration for achieving 100 mm chip size was validated which showed close agreement with the output produced using 2200SM model surface miner
Chemical characterization of PM10 and evaluation of health risk for the people residing around a highly mechanized opencast coal mine using FTIR spectroscopy
No full textAir pollution in opencast coal mine area is a very critical issue. The gradual increase in the demand of coal extrction leads to implementation of high mechanization techniques in most of the mines. Implementation of high mechanization techniques in mine produces huge quantities of PM (particulate matter), which disperse to the surrounding area of the mine and degrade the environment. Different mining activities like drilling, blasting, loading and unloading of coal and overburden material, transportation on haul road, etc. are the responsible sources of PM generation in the coal mine. Apart from these sources, local sources also have contributions to the total PM generation in the surrounding environment. Coal mine PM contains hundreds of chemicals which have adverse effects on human body and other animals also. The type of chemicals present in the PM depends with the change in the geographic location and method of extraction process. Quartz is a common mineral found in the atmospheric PM which has adverse effects on human body with inhalation. So many research works have been carried out on the characterization of PM to evaluate its risk on the human body. Measurement of quartz in the working area is also become a statutory need for all type of mines. The quartz present in the PM not only affects the health of the mine workers but also has evidenced to affect the people residing near to the mine area. The health effect of the PM depends on the type of chemical present. In this paper, an attempt has been made to measure the PM10 concentration around a high mechanized opencast coal mine in India, and the seasonal variations were studied. Characterization of the PM10 was also performed to find out the functional groups by using FTIR spectroscopic technique. The FTIR analysis showed the presence of hydroxyl, methyl, carboxylate, aldehyde, inorganic carbonate, sulfonate, etc. in the PM10 of the study area. Mineralogical study also was done along with the quantification of quartz in different seasons of the study period. Finally, the health risk was evaluated for the people residing near the mine area due to the presence of quartz in the respirable air. From FTIR studies, it was inferred that strong mineral band of quartz, kaolinite, sepiolite, cerussite, and nacrite was present at all the stations. The concentration of quartz in the study area was found above the prescribed limit (6 μg m−3) recommended by USEPA for healthy air to breath. The health risk assessment due to quartz in respirable air showed high level of risk in all the stations of the study area. Winter season was found to be the riskiest among all the seasons in the year in terms of the presence of quartz in respirable air. This study made is unique as it was done to evaluate the health risk for non-occupational people in the study area
Estimation of rock load for junctions based on roof failure cases for safe mining operation
No full textCoal mine roadway junctions in bord and pillar mining, in particular, are more vulnerable to roof fall due to the excavation induced stresses as well as general stress loading pattern inherent to the typical cross section achieved in practice. Roof fall incidences are generally more in junctions of development galleries and a cause of concern as they provide access to faces in different directions (dip/rise). The CMRI-ISM rock mass classification system, popularly known as Rock Mass Rating (RMR), is being used for the design of support system in underground coal mines for the last 30 years in India. In spite of the well-defined guidelines, it has been observed that roof failures are still a major concern in many underground coal mines. In this research, an attempt has been made to develop a new rock load prediction model for junctions of bord and pillar workings based on the geoengineering investigations carried out in 63 coal mines. After analysis of failure and stable cases, a best suited rock load predictor equation was developed. Analysis indicated that the maximum roof failure cases occurred for RMR values in between 30 and 45, and this zone is considered as highly unstable zone. Assessment of stable and unstable class is also done with respect to rock load for varied RMR. A general support design has also been suggested as per the RMR and severity of the roof fall. The suggested approach can help designing a rational support system for underestimated and overestimated zones thus minimising the roof fall cases leading to improved safety and productivity in underground coal mines
Elucidating the distribution and sources of street dust bound PAHs in Durgapur, India: A probabilistic health risk assessment study by Monte-Carlo simulation
No full textSpatial and seasonal distribution of PAHs, source identification, and their associated carcinogenic health risk was investigated in street dust of Durgapur, India. Street dust is an important indicator to detect the quality of the environment as well as the sources of pollutants. The obtained results showed fluctuation in PAHs concentrations from 2317 ± 402 ng/g to 5491 ± 2379 ng/g along with the sampling sites. Seasonal variation revealed higher PAHs concentrations in the winter season (5401 ± 993 ng/g) with the maximum presence of 4-ring PAHs. Two-way analysis of variance (ANOVA) exposed that the sites, seasons and site-season interactions were vividly affected by dissimilar PAHs. The PAHs source identification was investigated by principal component analysis (PCA), positive matrix factorization (PMF), diagnostic ratios, and they revealed pyrogenic, diesel, gasoline, wood and coal combustion to be the key sources of the PAHs in street dust. Obtained results from incremental lifetime cancer risk (ILCR) model exhibited the carcinogenic risk for children ranged from 2.4E-06 to 3.8E-06 while 2.1E-06 to 3.4E-06 for adults which were above the baseline value 1.0E-06. The Monte Carlo simulation model identified cumulative cancer risk of sixteen PAHs in 50th percentile were 2.8 and 1.7 times more while in 95th percentile, the values were 8.8 and 7.8 times higher than the acceptable value of 1E-06 for child and adult respectively