Emission factors for the quantification of dust in by jgb13951

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									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. A
search into the technical literature available on the       References
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