Characteristics of air-borne dust emitted by opencast coal mining in Jharia Coalfield
M K Ghose* & S R Majee
Centre of Mining Environment,lndian School of Mines,Dhanbad 826 004, India
Received 31" July 2000; revised 19 June 2001; accepted 20 June 2001
Opencast coal mining creates more air pollution problems in respect of dust and the fines contain coal particles, benzene soluble matters, etc.An investigation was conducted to evaluate the characteristics of the air-borne dust due to opencast coal mining. The study area has been described and the sources of air pollution were identified.Approach for the selection of air monitoring stations to assess the level of air pollution due to coal mining activities at different areas have been described.
Suspended patriculate matter (SPM) concentration was found to be very high in work zone and surrounding locations.The status of air pollution in respect of diurnal and seasonal variations have been discussed. The SPM was subjected to particle size analysis by using different techniques. It was observed that the particulates were more respirable in nature and the median diameter was around 20 J..l. Dispersion of these finer particles was causing pollution problem at longer distances.
Work zone was found to be more deteriorated in respect SPM, respirable particulate matter (RPM) and benzene soluble matters. Variations of weight percentages for different size ranges have been discussed on the basis of mining activities.
Benzene soluble and anion fractions in SPM were found to be high in comparison to other areas.The characteristics of the air-bone dust have been discussed in respect of human health hazard and air quality standards.
In India, coal production will have to be increased to meet the energy demand over the next 20-25 years at the rate of 20-25 Mt/y. To maintain the energy demand and overall coal production, opencast coal mining has grown at a phenomenal rate and in 1995- 96, when the country produced 274 Mt, the opencast mines have accounted for 68% of the coal production in the country. By 2000 AD, the coal production from opencast mining rose to 250 Mt which was about 70%
of the total coal production 1• In underground coal mining the miners suffer from coal dust inside underground mine workings. But in opencast mining, air pollution problem is much more acute particularly in respect of dust pollutants. In opening of opencast mine, massive over burden (OB) will have to be removed to reach the mineral deposit. These may require excavators, loaders, dumpers, conveyor belts, etc. which will result in massive discharge of fine particulates from OB material. Similarly normal operation will require excavation, size reduction, waste removal, transportation, loading, stock piling etc. All will release particulate matter. Closure is also similar to opening but for a short period2. Cowherd3
*For correspondence: E-mail: Ghosemrinal@hotmail.com
reported that vehicular traffic on haul road of mechanised opencast mines can contribute as much as 80% of the dust emitted.Chadwick et a/.4 estimated that about 50% of total coal dust released was during journey time on an unpaved haul road, while it was 25% for both during loading and unloading of dumper. Drilling is perhaps the next important source of fugitive dust5. Another major source of fugitive dust is wind erosion from coal stock piles.
Generally, the fines produced by opencast coal mining operations contain coal particles and dust particles. The average size of fines produced depend on different working sites. Central Mining Research Station, Dhanbad (CMRS)6, reported that the specific gravity of fines produced in coal washery vary from 1.23 to 1.7, average loss on ignition was 8-10% and free carbon 15-20%. Ghose and Banerjee 7 reported that in coal washery particulates were respirable in nature and more hazardous to human health. The benzene soluble matter and lead concentration in suspended particulate matter (SPM) were also found to be alarmjng. As the production of coal by opencast mining is growing, it is essential to evaluate its impact on air environment as also to assess the characteristics of the emitted air-borne dust, which is harmful to
418 INDIAN J. CHEM. TECHNOL., SEPTEMBER 2001
Stn. No. Station site
Table !-Location of work zone monitoring stations Location
BWI BW2
Feeder breaker Haul road (HR I)
Roof of feeder breaker control room at about 3 m above the ground
At a height of about 2 m on the debris at one side of the haul road
BW3 BW4
Haul road near box cut 3 section (HR2)
On the other side of haul roard near the box cut 3 office at about 3 m above the ground
Dragline section BWS Shovel/dumper loading
BW6 Workshop
At a distance of 100m from the dragline and at about 2 m above the ground
On the other immediate above the bench of a working bench
Roof top of a room near the workshop area, which was about 3 m above the ground
Table 2- Locations of different ambient air monitoring stations Stn No. Station site Nature of area
BAI Block II OCP Industrial
BA2 Benidih OCP survey office Industrial
BA3 Nudkhurkee Residential
BA4 Madhuband Residential
BAS Benidih hospital Sensitive
human health and vegetation. These data are essential for the effective design of air pollution control equipment like cyclone separator, scrubber,sprayer nozzle, etc. which are generally used in mining areas and also setting a rational air quality standard for coal mining areas. This paper envisages the fact finding survey for the evaluation of the characteristics of the air-borne dust emitted by one of the largest opencast coal project in Jharia Coalfield.
Coal Mining in Jharia Coaltield (JCF)
The Indian reserve of coking coal is mainly located in JCF of Bharat Coking Coal Ltd (BCCL). Coal exploration started in this coalfield intensivell in 1925. There are about 25 workable seams, each of 1.2 m or more in thickness making up a total of over 70 m. All of them are low in volatile content and are of coking quality. Generally seams I to IX are of inferior quality with an ash content of 20% or above, seams X to XVIII are of superior quality with ash content of less than 20%. These are prime coking.coal. Coal Council of India 9 estimated that, seams 0.5 m and above in thickness and up to a depth of 610 m are 13402 Mt, out of which about 5160 Mt are classified
Direction from Block II OCP Location
On the roof top of the Block II pit Centre office at which about 4 m above the
ground level
E On the roof top of the survey office at about 4 m above the ground
w
On the roof top of a villager's house at about 7 m above the ground SE On the roof top of a villager's houseat about 3 m above the ground NW On the roof top of the hospital at
about 4 111 above the ground
as prime coking, 2100 Mt are medium coking and the rest are non coking coal. The estimate of reserves up to 1219 m depth is 19339 Mt. JCF is covering for about 38 km east-west and 19 km north-south. The coalfield is subjected to intensive mining activities, because of easy availability of coal at shallow depth, in thick seams. This field is divided in 14 areas and each area is having a number of opencast and underground mines and accounts for more than 30%
of the total Indian coal production and produces about 27000 t of prime coking coal per day. It is one of the most polluted coalfields due to intensive mining activities and mine fire.
Details of the Opencast Coal Project (OCP) Under Study
The study area is one of the largest OCP for coking coal in JCF. It has 34.6 Mt quarriable reserve of coal.
The project report sanctioned in the year 1982 for a targetted production of 2.5 Mt/y and the life of the project was 17 years. The quarry was being worked in two patches through separate box cuts. Working depth during the study period was about 60 m in box cut 3 section. Working was going on in X seams having
NODKHURI O.CP.
BfNIDIH O.f.P
Fig. \-Location of air monitoring stations in the project area
>
a: w cr
11'1. z >-
<tcr
~~ ::.:~
~~
::>0 :.:'-' a.
Table }--Work zone air quality at different sampling stations during different seasons, 24 hourly average in )lg/m3
Stn. No. Winter season Summer season Monsoon season Post monsoon
SPM RPM SPM RPM SPM RPM SPM RPM
BWI 1638.9 409.6 1535.2 281.9 537.1 141.7 643.8 156.2
BW2 2437.8 557.1 2554.6 619.9 971.0 184.4 1874.7 352.2
BW3 1286.4 223.9 1179.2 194.1 556.6 108.8 1025.3 178.0
BW4 3723.5 780.1 3163.6 659.4 2200.7 473.8 2359.3 504.6
BW5 1640.0 278.5 1343.5 225.5 484.3 86.9 I 051.2 189.7
BW6 1005.6 195.7 1090.9 177.0 395.5 73.3 669.2 125.0
SPM-suspended particulate matter; RPM-respirable particulate matter
seam thickness 9.62 m. The project is located in the north-west of JCF in Dhanbad, Jharkhand. It covers an area of about 6.8 sq. km. It is located between latitudes 23°46'30"N and 23°47'4"N and between longitudes 86° I 0'4 7"E and 86° 13'31 "E. It is surrounded by many opencast and underground coal mines. The main drainage of the river is through Jamuni river.
(iii) Due to the movement of heavy vehicles on
The main sources of air pollution in the area are (i) Drilling and blasting
(ii) Loading and unloading of coal and over burden (OB)
haul road
(iv) Dragline operation
(v) Crushing of coal in feeder breaker (vi) Wind erosion
(vii) Presence of fire
(viii) Exhaust of Heavy earth mover machine (HEMM).
Methodology Adopted
Work zone air quality monitoring stations were selected near the sources of air pollution 10. The details of the monitoring stations are given in Tables 1 and 2,
420 INDIAN 1. CHEM. TECHNOL., SEPTEMBER 2001
and in Fig. 1. Ambient air monitoring stations were selected keeping in view the dominant wind directions prevailing in the area. One ambient air monitoring station was located in the project office of OCP. The dominant wind directions of the area were west and
h II !? D . h I . f b' .
nort -west · -. unng t e se ectiOn o am 1ent mr monitoring stations the approach was to put two monitoring instruments at upwind (west and north- west) and two instruments at downwind (east and south-east) directions. The approach was also to see that these should cover the industrial, residential and sensitive areas like hospital, as different standards have been laid by Central Pollution Control Board (CPCB)13 . The sampling was continued for twice in a week for four weeks in a month of each season covering winter (January), summer (May-June), monsoon (August) and post-monsoon (October) seasons14· Air samples were collected for 24 h in three 8 h shifts corresponding to day time , evening time and night time. Micrometeorological data were collected on sampling days with respect to wind direction, wind velocity, humidity and temperature15·16• For the collection of SPM samples, glass fibre ambient (GF/A) filter paper was used in high volume sampler(HVS) manufactured by MIS Envirotech, New Delhi. The flow rate for collection of samples was maintained at 1-1.5 m3!Inin. The collected SPM was analysed for physico-chemical characteristics, and the parameters selected for analysis are (i) particle size analysis, (ii) benzene soluble matter (tarry matter) and (iv) inorganic constituents (concentration of water soluble ions like S02, N03, Ch).
Particle size analysis of SPM was done on the basis of the principle of photo extinction and sedimentation with a Micron Photosizer manufactured by Seisin Enterprise Co. Ltd., Japan (Model SKN 1000).
Attachment of centrifuge with the unit had made it possible to determine size distribution down to 0.02 11·
Respirable dust sampler (RDS) make Envirotech, New Delhi was used to determine respirable particulate matter (RPM). In RDS, the dust laden air is imparted with a rotating motion by virtue of its tangential entry into the cyclone. Due to this rotation dust particles having size more than 10 11 deposits on the walls of the cyclone and settles below and the air containing the RPM travels up and collected over GF/ A filter paper. Particle size analysis was also done by cascade impactor, (make Graseby, Anderson, U.K.).
Benzene soluble matter was estimated according to IS: 5182 (part XII)17,. The inorganic constituents of SPM were analysed by standard methods. For this purpose, part of the SPM deposited on the filter paper was placed in a thimble and the benzene extract was prepared using soxhlet apparatus and redistillation method. The extract was concentrated to a small volume of 5 ml and the remainder of the solvent was removed by heating. The difference of weight in the container with the residue and blank gave the benzene soluble matter in the sample. Water soluble nitrate content was analysed by xyenol method, chloride by turbidimetric method and sulphate content by glycerol-alcohol method. Micrometeorological condi- tions were recorded on sampling days with respect to wind direction, velocity, humidity and temperature.
Results and Discussion
The results of the work zone air quality are given in Table 3. Maximum concentration of SPM was found in the dragline section. The next higher concentration was observed at haul road. Due to wind erosion these dusts cause more problems in opencast projects. Box cut 3 office near the haul road showed somewhat lower SPM concentration than the haul road (BW2l. It may be due to the spraying of water on haul road near this office. Feeder breaker unit also showed higher SPM concentration. During monsoon SPM concen- tration was found to be the lowest, but still at almost all the locations SPM concentration exceeded the permissible limit specified by CPCB,.for industrial zone (500 )lglm\ It was observed that SPM concen- tration during day time was found to be the highest in comparison to other two seasons. It may be due to the fact that major activities were done during general shifts (i.e. from 8 to 17 h). The results of the respi- rable particulate matter (RPM) also showed higher concentration and the highest during summer season.
The results of the ambient air quality of different samples are given in in Table 4,.which provides the status of air pollution during the year. The data reveal that SPM concentration at almost all the locations exceeded the permissible limits specified by CPCB during winter, summer and post-monsoon periods.
During the monsoon period SP'M concentration was found within the permissible limit due to removal of dust particles with rain water. lin fact they exceeded the permissible limits specified for industrial (500 )lg/m3), residential (200 )lg/m3) and hospital (1 00 )lglm\ RPM concentration in industrial location (BAI) also exceeded the permisible limit
Table 4--Ambient air quality at different sampling stations during different seasons Sampling Winter Season Summer Season
Station Range Mean S.D Range Mean S.D
Monsoon Season Range Mean S.D
Post Monsoon Range Mean S.D
Yearly average SPM Concentration in J..lg/m3
BAI 76S.6- 837.1S 73.38 S33.6- S93.87 S3.16
986.9 6S0.3
BA2 SS2.7- 6S4.17 64.19 S66.7- 618.97 47.17
7S4.S 709.0
BA3 380.9- 414.83 20.18 370.8- 398.79 18.99
4Sl.S 423.2
BA4 246.8- 304.29 31.67 342.S- 414.9S S7.04
342.7 493.1
BAS 207.8- 24l.OS S0.6S 97.S- 118.76 21.32
26S.6 1S7.8
297.8- 392.6 1S8.1- 2ll.9 93.0- 212.0
86.7- 212.3
73.8- 96.0
336.SI 183.97 IS2.04 133.18 86.18
30.89 473.7- S2S.43 43.3 S72.74 S8S.l
16.31 398.0- 443.66 29.67 476.69 29S.8
41.9 292.7- 312.48 27.43 319.S3 367.8
46.93 383.1- 441.87 34.63 323.S7 488.6
8.72 102.3- IS2.73 33.03 149.68 211.7
RPM concentration in J..lg/m3
BAl 1SS.8- 169.72 22.S7 106.1- I 19.SO 12.69
222.S 128.1
BA2 110.8- 133.30 16.6S I 12.1- 127.02 12.27
1S7.3 147.4
BA3 80.8- 91.10 6.40 8l.S- 86.73 3.9S
100.9 92.1
BA4 SO.O- 61.37 S.94 69.2- 89.37 I I .4S
67.1 101.8
BAS 42.3- 48.14 S.04 20.2- 24.08 3.76
SS.2 31.1
120, - - - -- - - -- -- --,
100
~
lii" 60
c Cl. ~
20
-+- Haul road SPM --o-Feeder breakn SPM
10 20 60 eo
Particle Size t!Jl
Fig. 2-Wind rose diagram during different seasons
100
( 150 j..lgim\ Wind rose diagrams for different seasons are given in Fig. 2.
SPM collected during summer (May-June), monsoon (August), post monsoon (October) and winter (January) from both ambient air zone and work zone were subjected to particle size distribution with a
SS.7- 77.6 30.3- 46.0 20.8- 47.3 I 7.4- 28.4 18.7- 23.8
66.74 37.17 33.48 23.26 2l.S3
7.SS 4.SI 8.88 3.69 1.84
89.0- 100.91 11.07 I 14.66 I 17.9
8S.8- 96.S2 7.64 98.SO 108.S
62.3- 68.4S 6.2S 69.94 81.4
76.9- 92.4S 8.SS 69.1 I 1036
21.4- 30.68 6.26 31.10 4l.S
Seishin Micro Photosizer and the results are shown in Table 5. Results of average size distribution of SPM m work zone air and ambient air have also been shown m Fig. 3. From the data it is evident that particle size less than 10 ll was 20-26% of total SPM in work zone air and was 18-23% in ambient air.
Thus work zone air is more dangerous in respect of respirable fraction of dust. It was found that both the zones were having less weight percentage having particle size above 60 11 size.
The analysis of work zone SPM sample for particle size, revealed that the weight percentage lying within different size range were the function of mining activity. The weight percentage of respirable function in haul road SPM was found to be more than that of feeder breaker SPM. This may be attributable due to continuous crushing and release of fine dust in haul road while only one crushing was done in feeder section. The dragline section, loading section also showed higher fraction of respirable dust in comparison to feeder breaker and workshop.
The results of RPM monitored by RDS revealed that work zone air were having higher concentration of RPM. Dragline section represented highest annual average of RPM concentration (604.50 j.lgim\ The annual average RPM concentration were found to be
422 INDIAN J. CHEM. TECHNOL., SEPTEMBER 2001
1-2 u 1.9-78
3- u 15.83
SA 1
SAl.
0-1 u 3-38
1.-5 u 17-39
0-1 u 8.73
1.-Su 11..67
Fig. 3- A verage particle size distribution of SPM in the work zone mr
haul road 463.36 ~g/m3, feeder breaker 204.85 ~g/m3, shovel/dumper loading 195.09 ~g/m3 and at workshop 297.79 ~g/m3. The results obtained by RDS are comparable with those of Micron-Photosizer value.
The concentration of RPM exceeded the permissible limit (150 ~g/m3) during the winter (169.72 ~g/m3) at station BA 1. Particle size analysis by cascade impactor shown in Table 3 indicates that out of the size range 0-2 ~. at ambient air station BA 1 (industrial) was having weight percentage of 48.16%
and at BA4 was 54.5% (residential). This may be attributable to dispersion of more finer particles to longer distances at residential zones. The results
Table 5--Particle size analysis of SPM with the use of Micron Photosizer
Size range Percentage b;t weight in the range (micron) Ambient air Feeder breaker Haul road
0-2 5.4 3.8 5.9
2-5 5.3 4.5 5.3
5-10 8.5 10.6 12.1
10-20 31.2 28.7 26.2
20-40 28.6 42.3 36.0
40-60 15.5 7.2 11.3
>60 4.6 2.9 3.2
Table 6--Particle size analysis of particulate matter by Cascade Impactor
Particle size Percentage EJ.~eight (micron) Station BAI Station BA4
0-1 3.38 8.73
1-2 44.78 45.77
2-3 13.62 16.93
3-4 15.03 13.90
4-5 17.39 14.67
Table 7- Benzene soluble fraction in SPM
Ambient zone Work zone
Station BSF% Station BSF%
BAI 21.2 BWI 24.0
BA2 29.3 BW2 31.8
BA3 16.7 BW3 28.5
BA4 17.6 BW4 19.1
BA5 I 1.0 BW5 16.2
Table 8-Anions in ambient air SPM Station Average anion concentration(%)
so4 N03 Cl2
BAI 3.89 0.20 0.57
BA2 4.40 0.19 1.82
BA3 2.35 0.11 1.02
BA4 2.17 0.09 0.56
BAS 1.60 0.06 0.41
obtained by cascade impactor (Tables & 6) are comparable with these obtained: by Micron photosizer.
It was observed that the median diameter of SPM was around 20 ~. which indicates that the particles are finer in nature and more hazardous to health. The study also reveals that due emphasis should be given to particle size distribution while adopting air pollution control measures and these data may be useful for proper designing of air pollution control equipment for coal mining areas.
Benzene soluble matter ranged from 1 J to 30% in ambient air and 16 to 32% in work zone air (Table 7).
WINTER SEASON
N
w
SE
s
MONSOON SEASON NW
N
w
sw
s
sw
w
SUMMER SEASON N
s
POST-MONSOON SESON
N
s
Scaleo-1 em,= S% .
1
~
- 7 - 14 - 28W1nd 5pet>d krn/h
SE
E
SE
Fig. 4- Average particle size analysis by Cascade Impactor
The maximum concentration was found at industrial location (BA2) and at haul road (BW2). This high value indicates the probability of more serious health hazards as it is carcinogenic in nature. The results of anion concentrations on ambient air in Table 8 showed that the sulphate content varied from 1.6 to 4.4%, nitrate content 0.06 to 2% and chloride content from 0.4 to 1.9%, maximum concentrations were observed at industrial location BA2.
Conclusion
Due to opencast coal mining the work zone as well as ambient air were found to be highly polluted in respect of dust. The respirable fraction , anion concentration and benzene soluble matter in SPM were found to be alarmly high and may effect human health. Dispertion of these finer particles creates serious problem in and around mining complexes.
The study reveals that more stringent air quality
424 INDIAN J. CHEM. TECHNOL., SEPTEMBER 2001
standards should be adopted for coal mmmg areas which will prevent harmful effects to human health and vegetation. These data may be useful for the effective design of air pollution control equipment for coal mining areas. The methodology adopted may have formed a guideline which may be utilized on industrial scale for various sites.
Acknowledgements
The authors are thankful to the Ministry of Environment and Forests, Govt. of India, for supporting grants for infrastructral facilities at Centre of Mining Environment, Indian School of Mines, Dhanbad. Financial support in the form of fellowship received from University Grants Commission by the author (SRM) is greatfully acknowledged.
References
I Kumar U, Transactions, 92 ( 1995) I.
2 Ghose M K, Minetech, I 0 ( 1989) 91.
3 Cowherd C Jr. Measurements of Fugitive Dust Emissions From Haul Roads, Report No. EPA-600/7-79-182, Research
Triangle Park,. NC: USEPA, Industrial Environmental Research Lab. ( 1979).
4 Chadwick M J, Highton N H & Lindman N, Environmental Impacts of Coal Mining and Utilisation (Pergamon Press, UK), 295.
5 Nair P K & Sinha J K, J Mines Met Fuels, 35 ( 1987) 360.
6 CMRS, Dust problem due to washe , Central Mining
· Research Station, Dhanbad (1961 ).
7 Ghose M K & Banerjee S K, Energy Environ Monitor, 13 ( 1997) II.
8 Fox C S, The Jharia Coalfield Memorandum, Geological Survey of India, 56.
9 Coal Council of India, (1963).
10 Ghose M K & Banerjee S K, Environ Monitoring Assmt. 38 (1995) 97.
II Ghose M K & Sinha D K, Indian J Environ Protec, 10 (1990) 752.
12 Ghose M K, Majee S R & Sinha P K. lnt J Environ Studies, 56 (1999)1.
13 Banerjee S K, Dhar R K & Ghose M K, Environ Mgmt, 20 ( 1996) 236.
14 Ghose M K & Majee S R, Atmos Environ. 34 (2000) 2791.
15 Ghose M K & Majee S R, Minetech, 21 (2000) 48.
16 Ghose M K & Majee S R, Environ Monitoring Assessment, 61 (2000) 255.
17 IS:5182 (Part XII) Indian Standard Methods for the Measurement of Air Quality ( 1974 ).
