Journal of Scientific & Industrial Research Vol. 63, September 2004, pp. 763-768 Emission factors for the quantification of dust in Indian coal mines Mrinal K Ghose Center of Mining Environment, Indian School of Mines, Dhanbad 826 004 Received 24 August 2003; rev recd 01 June 2004; accepted 05 July 2004 The increasing trend of opencast coal mining tends to release huge amount of dust. But there is no well defined method of estimating dust emission due to coal mining activities This paper examines the sources of dust emission due to coal mining activities and focuses on the quantification of dust emission with the use of emission factors or prediction type equations. Because of site-specific nature, emission factors developed for one site may not give the correct results for another site. In the present investigation prediction equations are utilized for the development of emission factors and they are used for the quantification of dust generation due to opencast coal mining. For the applications of this concept one large opencast coal project of Bharat Coking Coal Ltd (BCCL) was investigated and the amount of dust emitted due to different mining activities was quantified. This paper also focuses on the significance of this study in the field of environmental protection and likely impacts of such study. The paper concludes that once the amount of dust generation is estimated, the impact on air quality can be assessed appropriately and a proper air pollution control strategy can be developed. Keywords: Opencast, Dragline, Box cut, Hauls road, Prediction equations, Batch load IPC Code: Int. Cl.7 : C 09 C 1/44 Introduction Emission Factors The main air pollution problem in a mining area is In coal mine planning, an estimate of dust due to the presence of particulates, which may be generation is to be made to check the likely level of coal, soil or rock dust1. Strip mine air pollution source air pollution in the mining area due to proposed can be divided into two categories, point sources and project activities. Typically this can be obtained by fugitive sources. Points sources typically include using emission factor or prediction type equations. stationary exhaust stacks2. In contrast fugitive sources Jacko7 gave estimates of fugitive dust from some are open sources like the exposed soil of OB and mining activities. Emission factors from surface coal coal3. Vehicular traffic on haul road has been mining operations in the Power River Basin of identified as the most prolific source of fugitive dust Wyoming Surface Mine8 includes emission factor and can contribute as much as 80 per cent of total data as a function of distance from the source. The dust. Cowherd et al.4 estimated that about 50 per cent U.S. Environmental Protection Agency (EPA) of the total dust released during journey time of published a compilation of air pollution emission dumper on unpaved haul road while 25 per cent for factors (commonly referred as AP-42), a handbook, both during loading and unloading of dumper. which use the A to E quality rankings. Mayer9 Chadwick et al.5 estimated that 0.02 per cent of the originally developed the compilation of emission coal is lost during loading and unloading. Nair and factors from the technical literature and a report. More Singh6 estimated that road dust contains more than 4 editions appeared including Duprey10 and USEPA11,12. per cent of respirable dust. Another major source of Sinha13 illustrated the technique of exposure profiling fugitive dust is wind erosion from stockpiles. Jacko7 method, specially designed and fabricated for the has given estimates of fugitive dust from mining study to develop methods to quantity fugitive dust operations. The workers are exposed in opencast emission for vehicular traffic on unpaved haul road. mining varies between 3–5 mg/m3 in coalfaces and 1–2 mg/m3 in overburden faces. After haul road, Prediction Equations drilling: b perhaps the next important source of The above-mentioned norms are thumb rules only. fugitive dust. During drilling in overburden benches Because of site-specific nature of dust, emission the dust concentration varies between 20–25 mg/m3 factors derived for one site may not give the correct and in coal benches it varies between 15 – 30 mg/m3. results for another site. Many factors such as 764 J SCI IND RES VOL 63 SEPTEMBER 2004 brittleness and hardness of the materials being (c) Unpaved Haul Roads handled, clay or silt and moisture content of the rock Cowherd et al.16 suggested the use of the following material, wind speed of the region, the size of the equation for estimation of particulate emission from earth moving machinery in operation control the haul trucks on an unpaved road surface. amount of dust being formed and dispersed in the area. The prediction equations14 give better estimation eu = 5.9 (S/12) (S/30) (n/3)0.7 (W/4)0.5 (d/365) of dust formation in opencast mines. A few prediction equations are given below. where, eu = Unpaved road emissions as lb-particulates (a) Continuous Load in Operations vehicle make travelled (Particles smaller than 30µ Bucket wheel excavators with stacker conveyors with a density of 2.5g/cm3) are being used in many of the surface mines. The S = Slit content per cent, following equation allows in estimation of the fugitive V = Average vehicle speed, mi/h, particulate emissions from such an operation15,16. W = Average vehicle weight, t n = Average number of vehicle wheels, e 0.0018 ( S / 5)(U / S )(h /10) d = Number of dry d/ y cont. in = , ( M / 2) 2 (d) Active OB Storage Pile wind Erosion e where, pile = 0.05 (S/1.5) (d/235) (F/15) (D/90) e cont.in = Particulate emission expressed as lb/ton where, of materials loaded in, F = per cent of time unobstructed wind speed S = Silt content of aggregate or road surface exceeds12 mph at a mean pile height, materials per cent, D = Duration of material storage,d. U = Mean wind speed 4m above the ground, mi/h, Applications h = Drop height (ft), The indigenous coking coal production in India is M = Unbound moisture content of material per not fulfilling the demand of steel industry for which cent. about 7 Mt of coking is being imported annually17. (b) Batch Load in Operations The extraction of coking coal is increasing rapidly to Included in batch load in operations are the meet the demand. Block II OCP, one of the largest dragline, front-end loaders and rail car dumping. The opencast projects of coking coal owned by BCCL, equation was originally developed for front-end was selected for the application of this work. It has loaders, rail car dumping operations for shovel, but 34.6 Mt quarriable reserve of coal. The project report has been extrapolated for dragline15,16, was sanctioned in the year 1982 for a targeted production of 2.5 Mt/y and the life of the project was e 0.0018 ( S/5) (U/5) (h/5) 17 y. The quarry was being worked in two patches batch - in = , ( M/2) 2 (Y/6) 0.33 through separate box cuts. Working depth during the study period was about 60 m in box cut section 3). where, Work was going on in X seam having thickness 9.62 e batch-in = Emission expressed as lb/ton of m. The project is located in the northwest of JCF in materials loaded in, Dhanbad, Jharkhand. It covers an area of about 6.8 U = Mean wind speed 4m above ground, mi/h, sq km. Many other opencast and underground coal h = Drop height, (ft), mines surround it. The main drainage of the region is M = Unbound moisture content per cent, through Jamuni River. The region has a tropical Y = Dumping device capacity, yd3, monsoon type climate. The general wind direction is S = Silt content per cent, from the west with few clouds from December to For a 100-yd3 dragline operating on a material with February. Air originating from the sea to the east and S = 13 per cent, M = 8 per cent, at 8 min/h wind speed the south brings about 80-85 per cent of annual and 60 ft drop height. rainfall in June through August. The winter season e batch-in = 0.0022 lbs-particulate/ton of material extends from November to February with temperature loaded in. as low as 5°C. The summer season is from March to GHOSE: QUANTIFICATION OF DUST EMISSION IN INDIAN COAL MINES 765 June and the highest temperature experienced is 48°C. Table 1 Emission factors evaluated for different mining The rainy season starts in late June and it ends in operations September. The southwest monsoon brings the major Source Emission factor precipitation. The annual rainfall in this region is (a)Overburden excavation 1197mm. Scraper loading No data Shovel excavation 1.0 to 3.0 kg/t Bucket wheel excavation 0.7 to 2.0 kg/t Methodology Loading in vehicles 0.7 to 0.4 kg/t The sources of dust generation were identified. The (b)Transportation 0.5 to 0.1 kg/t geological setting of the area was recorded. Different Conveyor belt machineries used for drilling, mining, removal of Each transit point *Dumper 1.5 to 3 kg/km of tunnel earthen overburden, transportation system were also recorded. Dumper dry surface Different mining activities like topsoil removal, * Total emission will be 0.1 to 3 kg/km of tunnel soiled kg/vehicle/km/d overburden removal, coal extractions, size reduction surface and total quantity handled per day in each case were (c )Unloading and Piling 0.8 to 1.5 kg/t also recorded. Parameters like mean wind speed, drop Conveyor system 1.5 to 4.0 kg/t height, unbound moisture content, dumping device Dumper-Bull dozer capacity, silt content, average vehicle speed, average (d) Mineral excavation 0.5 to 1.0 kg/t vehicle weight, average number of vehicle wheels, Bucket excavator 0.8 to 1.5 kg/t number of dry d/y percentage of time unobstructed Shovel 0.08 to 0.1 kg/t Loading conveyor belt vehicle wheels, wind speed exceeds 12mph at a mean Loading dumper Each travel point pile height, and duration of material storage were 0.07 to 0.3 kg/t average (e)Transport evaluated. Conveyor belt 0.05 to 0.1 kg/t The data obtained were put in the prediction Dumper /truck Each travel point equations developed for different operations and Dumper /truck 1.5 to 3.0 kg/km Travel dry emission factors were evaluated for each activity. surface Statistical average of the rate at which dust released as 0.2 to 0.5 kg/km Travel by soiled road a result of some activity were multiplied by that activity. Thus the rate of emission of dust per unit of a (f) Stock pilling/loading Conveyor 1.0 to 2.5 kg/t given activity was computed, which is known as the Dumper/manual 1.5 to 4.0 kg/t emission factor and expressed as per tonne of mineral mined, per tonne of mineral crushed, etc. An estimate (g) Size reduction Jaw crusher 1.5 to 2.5 kg/t was made for the number of such processes. The total Screening 2.5 to 5.0 kg/t emission then equals the product of emission factor Loading 0.8 to 1.5 kg/t times of the number of such sources. Emission thus Stock pilling and retrieval 1.0 to 4.0 kg/t will represent the best values for different mining activities. Typical air pollution factors thus obtained box cut section 3 and 40 per cent from the dragline are summarized and presented in Table1. section. In the box cut section 3, there were three OB Quantification of Dust benches equipped with 3 power shovels (10 m3 Opencast mining generates large quantities of dust capacity) and one coal bench with one power shovel. during its various operations. Different mining The average depth in this section was about 57 m. activities include topsoil removal, overburden There were three drill machines in this section. The removal, coal extraction, size reduction, etc. The mine dragline section was equipped with one huge dragline was producing 2500t of coking coal/d i.e. 0.75 Mt/y. (24 m3, 96 m) was handling about 40 per cent OB, i.e. during the study period. The stripping ratio was 3.98, 8990 t/d. The dragline was equipped to remove OB up i.e. 24875 t of OB was removed/d. Out of this, the to 35 m depth and side casted. In the box cut section average topsoil removal was 2400 t/d. The whole 3 OB was transported through along the haul road for OCP was divided into two parts one box cut3 about 0.5 km for dumping. The number of dumpers in section and one dragline section. During the study working condition was 15. After the removal of O/B period, 60 per cent of production of coal was from and exposure of the coal strata, coal benches were 766 J SCI IND RES VOL 63 SEPTEMBER 2004 Table 2 — Quantification of dust generated by using emission factor data Source Material TPM Unit Amount Remarks emission of dust factor generatio n kg/d 1 Topsoil removal Overburden 0.029 kg/t 69.6 Total OB to be removed =22475, average OB removed as topsoil =2400t 2 OB removal (a) Drilling Overburden 0.59 kg/hole 35.4 Av. number of holes = 60. length of hole = 13 m (b) Blasting Overburden (c) Dumper loading by power shovel Overburden 0.018 kg/t 242.7 OB handled by power shovel in Box cut-3 Sec (60 per cent) =13485 t (d)Transportation in haul road Overburden 2.25 kg/vkt 356.9 Length of haul road =0.5 km. Distance traveled by 85t dumper to transport 13485 t OB = 158.6 km (d)Unloading Overburden 0.001 kg/t 24.9 Total OB unloaded = 24874 t 3 Coal extraction (a) Drilling Coal 0.10 kg/hole 4.0 Av.no.of holes in a coal bench = 40, depth of hole = 10 m (b) Blasting Coal (c) Loading Coal 0.014 kg/t 35 Total coal loaded =2500 t (d)Transportation Coal 2.25 kg/vkt 135.4 Amount of coal loaded per day = 2500 t, length of haul = 0.7 km, distance traveled by 58 t dumper to transport 2500 t of coal =60.3 km (e) Coal unloading Coal 0.033 kg/t 82.5 Amount of coal loaded per day = 2500 t Sub Total 257 4 Size reduction (a) Crushing and coal feeding Coal 1.5 kg/t 3750 Av. amount of coal crushed daily to convenient size =2500t (b)Convey or belt Coal 0.075 kg/t 187.5 Length of conveyor belt = 90 m (c)Unloading point to bunker and Coal 1.15 kg/t 2875 chute to dumper Sub Total 6812.5 5 Wind erosion (a)Wind erosion of exposed area Coal 2.33 kg/ha/d 1569.2 Total exposed area = 673 ha Total dust generation =9366.7kg/d drilled, blasted and coal was transported to the generated 660.0 kg of dust/d; extraction of coal feeder breaker for size reduction. The coal was contributed about 256.9 kg of dust/d. Observation of crushed to -200 mm size by a feeder breaker. Coal dust generation due to size reduction contributed handled by feeder breaker was about 2500 to dust amounting to 6812.5 kg of dust/d. The mining 3000t/d. The crushed coal was transported to bunker activity generated dust amounting to 7799 kg of by means of a conveyer belt from which loading to a dust/day. Wind erosion also generated a huge dumper was done to dispatch to a railway siding. amount of dust of about 1569.2 kg/d. Blasting also The feeder breaker consists of a crushing unit, causes a huge generation of dust but due to transporting crushed coal by a conveyer belt, unavailability of emission factor data the actual unloading into a bunker, and loading from the quantity could not be estimated. For the calculation bunker to the dumper. of dust generation the emission factor data used are As calculated the dust generation by the shown in Table 1. The total amount of dust utilization of emission factor data, topsoil removal generated as calculated by the utilization of emission generated 69.9 kg/d. Overburden removal operation factor data was found to be 9368.2 kg/d (Table 2). GHOSE: QUANTIFICATION OF DUST EMISSION IN INDIAN COAL MINES 767 Significance of the Study Emission factor data thus developed can be utilized Environmental impact assessment (EIA) plays a for the prediction and assessment of dust generation crucial role on resolving the conflicts between due to coal mining activities. This study has an developmental objectives and concern for the immense significance in the field of environmental environmental quality. In fact EIA is considered to be protection and likely impacts of the findings are a valuable planning and decision-making tool for many. Once the amount of dust generation is prediction and evaluation. This has led to the estimated, the impact on air environment due to the preparation of environmental management plan project activities can be assessed appropriately and an (EMP) prior to the implementation of any project. The air pollution control strategy can be developed to system of preparing EMP has been accepted as a maintain the right kind of balance between sustainable statutory requirement for getting clearance from development and environmental management. It is Department of Environment (DOEn), Government of concluded that the study provides a sort of India. All such mining projects need to be cleared by fundamental scientific insight in the quantification of DOEn. To ensure the effective safeguard at the dust emission due to coal mining activities. designing stage against the environmental hazard, DOEn has issued guidelines for preparation of EMP Acknowledgements report for mining projects. Finally the Environmental The author is thankful to Ministry of Environment Appraisal Committee (EAC) for mining projects and Forests, Government of India, for supporting examines the report before giving any clearance to the grants for infrastructral facilities at Centre of Mining project18. Environment, Indian School of Mines, Dhanbad and Air pollution is one of the most important providing financial support for the work. Assistance parameters to be considered in preparing EIA report19. taken from Sri S R Majee at different stages of the But there is no well-defined method of predicting the work is also acknowledged. generation of dust due to different mining activities. 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