COAL MINE PLANNING & DESIGN -A.V.REDDY, ADDL.MANAGER The Singareni Collieries Company Limited
Mining Methods • Generally Coal is being mined by two main methods – 1. Surface or ‘Opencast’ mining 2. Underground mining. • The choice of method is largely determined by the depth, thickness and no. of coal seams, geology of the coal deposit and other factors.
Reconnaissance Survey To plan for winning any coal deposit, the required data/Information is 1. Geological Report of the Block 2. Surface features exists in and around the deposit
1.Geological Report / Geo-Model Geological Report will be generated basing on the detailed exploration of the deposit. The Borehole data generated with detailed exploration will be used for preparation of Geological Report. Many soft wares are available for generating geological report and the report generated through soft ware is called Geo-Model. MINEX, SURPAC, DATAMINE are some of the soft wares currently being used for preparation of GeoModel.
What is Geological Report / Geo-Model? Geological Report / Geo-Model consists of
• • • • • • • • • •
Surface Topography – Hills, contours, rivers of Flats Geological Map – in crops, Faults Graphic Lithologs Graphic correlation charts Floor/Roof contour plans of all seams Seam folio plans of all seams (seam out cop, floor contours, faults, Iso-UHV, Iso-chore, Iso-depth). Geological cross sections Seam structure of all seams ISO parting plans ISO excavation plan for lower seam (surface constraints, boundaries, faults at seam level, excavation area)
Additional data – Geological Report Geo-technical data - Diggability of materials, slope geometry and stability of Working/permanent slopes, spoil pile configuration for outside/inside dump, stability, grainsizes after blasting etc. Ground Water Hydrology
- Dewatering and depressurization Impact of dewatering on surrounding areas - Impact on water quality
Surface Hydrology
- Water quality - make off water - Mine flood protection - Options for discharge of dirty water and various discharge systems.
2.Study of Surface Features For opening up of any deposit, it is necessary to study the surface features within and around the deposit and the data which consists of Presence of villages/habitats - Densely populated areas Presence of rivers/Jores/nalahs/railway lines/roads etc. Type of land including land use - Forest/Non Forest Ecologically Sensitive areas like wild life sanctuaries, Bio reserves, National Parks and archeologically important structures/monuments Inter state/National boundaries Critically Polluted areas/Environmentally fragile areas
Conceptual Stage • After detailed study of Geological Report coupled with study of detailed surface features, a Conceptual Report will be prepared with various options. • A detailed review on Conceptual Report will be taken up before finalising the method of work to be adopted and the technology to be used. • After finalising the method of work, Detailed Project Report will be prepared which includes Technical and Financial feasibility.
Deposit Resources GR/MR Mining depth Strata Sequa Thickness of - coal - waste - inter burden Coal Quality Slope stability Water
Tech-Aspects
Mining Technology Options and Suggestions Equipment Surface Constraints
Economic aspects
Production requirements Minelife requirements Logistics, Roads etc. Cash out flow Cash inflow Required rate of Return Cut-off SR
Conceptual Mine Plan
Modification of concept and or optimization Pre-Feasibility Study
Accepted – DPR
Management
Not accepted – New attempt
1. Opencast Mining • Shovel Dumper Technology • Drag line-Shovel Dumper Technology Extended Bench method Spoil Bank method • In-pit Crusher & Conveyor Technology • Surface Miner Technology • Ripper - Shovel Technology • Rock Breaker Technology • High Wall Mining Technology 2. Underground Mining
Two types of access to the coal deposit for winning the coal with underground technology • Incline • Shaft • Adit
Underground Mining – Different technologies • Bord & Pillar Technology Manual Mining Semi Mechanisation with SDLs/LHDs/Scrapers Depillaring with caving Depillaring with stowing • Longwall Mining Technology Longwall advancing Longwall retreating Shortwall Mining • Blasting Gallery Technology • Continuous Miner Technology
Mining Methods Shaft Mine
Incline Mine
Incline
Excavator
Adit Mine
Opencast Mine
OPENCAST MINE PLANNING & DESIGNING
Ideal conditions for Opencast Mining 1. Thickness of coal seams-
> 5m
2. Flat gradient
-
< 1 in 6
3. Strike length
-
> 1 km
3. No.of seams
-
Less the better, with higher thickness
5. Coal without stone bands 6. Free from surface structures / features. 7. Preferably non-forest land.
8. Availability of adequate place for dumping. 9. Stripping ratio depending on quality of the coal
Basis for the initial study is Geological Report • There will be some overlap between various studies/reports. • Every step deals with Mining Technology, equipment, production scheduling, capital cost, revenue cost, internal rate of return, dispatches etc. However the degree of accuracy of data on the above aspects increases with each step.
• Generally After F.R. approval, there is need to go in for long term planning, medium term planning (about 5 years) and S.T.P. Short-term planning (6 months – one year). • These reports should adapt circular analysis approach by considering various aspects like additional information available while operating the mine, slippages occurred, reserves, pit-slopes, pit-limits, pit scheduling to control faster rate of extraction from coal inventory which otherwise may lead to reduction in coal production in subsequent years or more equipment for higher OB removal to maintain targeted production.
Steps in designing of Opencast A. B. C. D. E. F.
Study of deposit exploration (GR) Final pit limits. Development sequence. Design of Access Ramp and Haul Roads Pit design Annual production capacity – system availability – Mining technology G. Main Mining Equipment – Matching to Mining Plan H. Optimizing Dumping strategy and balancing I. Year-wise / Stage – Wise plans J. Financial viability (Capital & Revenue) K. Coal Washing L. Environment Stipulations
A. Study of GR on the deposit Exploration Salient Information •
Extent of deposit i.e. strike and dip rise widths.
•
Geology – Geological succession, sequence of beds, drilling, logging, no. of seams, sequence of coal seams, description.
•
Inter seam partings.
•
Structure – No. of faults, Throws, dip of seams and beds
•
Reserves – Quality wise/seam wise/depth-wise etc. based on Block model, Gridded seam model & polygonal Model
•
O.B. volumes & S.R. – Sector-wise, depth-wise etc.
•
Coal seam analysis, proximate and ultimate , Ash etc. & OB strata hardness etc.
•
Drilling details (Lithology)
•
Physiography
•
Climate and Vegetation
•
Preliminary EMP information
B. Final pit limits The criteria for delineation of boundaries of an Opencast Project Rise side boundary
- Usually incrop of the bottom most seam
Lateral sides
- Usually by Geological disturbances like faults, surface structures / features like nalah, river etc or limitation of the strike length of the deposits.
Dip side
- Depends on the economical stripping ratio, in absence of natural constraints
Haul analysis Lead, lift increase cost Dump area Dump limits
Mineable Reserves
Maximum depth
- Decides mode of transport -100m from mine boundary - Dump area - 50 m from internal access road. - Dump area - 80-100 m. from mine infrastructure - various losses, batter, barrier etc. - dilution etc (50 Cm against Roof, floor) - increases haul cost (30-40% of total cost at 1 1/2 Km lead)
B. Final pit limits Estimation of Coal, OB & Stripping ratio
Contd.
Rough assessment is given below • Assuming Pit slopes of 450, the Quarry floor and Quarry surface are delineated •
Volume of Coal & OB
•
Average area
= (Quarry surface area + Quarry floor area) / 2
•
Average depth
= (Minimum depth + maximum depth) / 2
•
Volume of Coal=(Quarry floor area x Cumulative thickness of all coal seams) - (B)
•
Coal in tonnes
•
OB Volume
= Average area x Average depth
- (A)
= Volume of coal x Specific gravity – (C) = Coal + OB Volume (A) – Coal Volume (B) - (D)
• Stripping ratio = OB Volume (D) / Coal in tones (C) For accurate S.R,the volumes of OB and coal are to be made seam wise
B. Final pit limits
Contd.
The boundaries are firmed up based on the economic stripping ratio. Economic stripping ratio varies with: • Average sales realization i.e. higher the quality of coal, higher the realization. • Capital investment requirements • Operating cost. • Also surface constraints The following thumb rules may be of some Help (with outsourcing OB removal): Projects are likely to be economically viable upto a maximum SR indicated against the grade of coal Grade
Stripping ratio (Cum/T)
F
6
E
7
D
8
C
10
C. Development Sequence Opening the deposit
– Access trench
Box cut
- To accommodate all equipment
Mine phases
- Depends on the shape of the property
Progress of Benches Coal production schedules OB excavation schedules
Note:- Maximize inventory of coal in the initial years • Differ OB stripping requirements as much as possible – Average SR versus natural SR • Income generated in the first 5 to 10 years but not remote economics will either make or break the project. • Profits for in the future have practically no impact on the project NPV. Each successive phase will be less profitable and the ultimate
limit will be loss even after ploughing in earlier profits.
D. Design of Access Ramp & Haul roads Location of Access ramp is guided by the following: 1)
Generally located at the minimum depth of incrop of bottom most seam – So as to reduce initial waste stripping (unproductive work)
2)
Should facilitate maximizing of internal dumping and sectional working.
3)
Should be near the External dump / Coal yard / Mine service facilities etc. Main haul road upto the pit limit should be planned in the beginning only. Since haul costs constitute about more than 40% and tyre costs about 10% of the total mining costs,priority for design,construction and maintenance should be given. Gradient,width,drainage,curves,super elevation,base,sub base,type and thickness of top dressing should be like that of national high ways for heavy traffic.
4) 5)
6)
D Contd.
D. Design of Access Ramp & Haul roads
Sl.No
Particulars
1
Width
Should facilities two way traffic, dozer movement, formation of drains, lighting arrangement (Normal width – 30m, but depends on capacity of dumpers).
2
Gradient
1 in 16
3
Lesser number of curves
4
In flat seams of larger Haul roads can be formed over the strike length floor of the seam
5
In steep seams
Haul road for Coal & OB benches can be planned along highwall slopes say every 30m. This will also facilitate internal dumping.
E. Pit design General design parameters and planning data • • • • • • • • • •
• • •
Density of seams, total coal column thickness Thickness of partings Gradient Geological disturbances Strike lengths, shape of property Geological Reserves Surface constraints/adjacent habitat Dump yards availability with lead and lift Mining system, optimum mining concept Depth of operation, mineable reserves after various losses, OB volumes, SR Spoil characteristics Work practices in the Area Diggability characteristics
E Contd.
E. Pit design As per Regulation 98 of CMR 1957, In alluvial soil etc.
-
Sides shall be sloped at 450 or Benched – height not more than 1.5m Width – not less than height
In hard ground
-
Sides adequately benched/sloped so as to prevent danger from fall of sides
Coal
-
Sides shall be sloped at 450 or Benched – height not more than 3m
However, exemption can be sought from Inspectorate.
E. Pit design
E Contd.
Overall slope of a pit depends on several factors of the pit slope: a)
Geological disturbances like faults etc.
b)
Hydrological condition of strata
c)
Orientation of slip planes
d)
Nature of strata – i.e. hardness, material consolidation etc.
e)
Depth of workings
f)
Design of haul roads & ramps in the highwall
g)
Stratigraphy – thickness, spacing of the clay bands or other weak layers
E. Pit design
E Contd. In general for OC mines upto a depth of 200m, overall slope angle of 450 is permitted.
E. Pit design
E Contd.
For deeper mines flatter highwall slopes will be necessary from safety point of view (for 35 T dumpers & above)
E. Pit design
E Contd.
For deeper mines flatter highwall slopes will be necessary from safety point of view (dumpers below 35T capacity)
E. Pit design Typical High wall layout
E Contd.
E Contd.
E. Pit design Working benches 1) General Width Height
- 40 – 45m - Generally equal to height of the boom or in some cases upto 3m above the boom height. In case of Backhoe – digging height of machine Bench slope - 560 to 700 2) Dragline: Width of the cut Height of bench
-
60m maximum digging depth
3) In order to even out the yearly OB removal quantities and the economics sometimes alternative workings and non-working benches (around 25 m wide) are proposed.
F. Fixing annual production capacity After defining the boundaries, the annual production capacity will be fixed based on the following criteria : 1)
The available mineable coal reserves
2)
Geometry of the deposit -
3)
Structure of the deposit -
Strike & dip rise lengths Thickness of seams, partings, faults, gradient etc.
4) Linkage
-
Basket, Captive use etc.
5) HEMM configuration
-
Capacity of HEMM.
6) Surface structures
-
Limits the material to be blasted.
G. Excavator machine productivity
G Contd.
–Based on , -Dipper cycle time -Waiting time for truck spotting -Bad blast factor -Truck loading time etc. Annual capacity is based on -Equipment available hours
-Utilization percentage Proper fragmentation,less throw off material,bench height,bench slopes ,avoiding toes and secondary blasting,improves shovel efficiency
Optimum fragmentation-cost of drilling,blasting vis-à-vis cost of dozing,loading,hauling and dumping.
G Contd. System availability as a function of individual components Calendar hours-(365x24)
(Figures are Indicative only)
Holidays and bad weather
2.5%-
Operational delays-blasting, relocations,shift change,Lunch etc
1 Hour/Shift(8%)
Preventive maintenance-i.e annual,weekly,daily,shift wise and unexpected break downs
15% of SSH Availabilty-
Shovel,dumper system 12% - Crusher + 1 Conveyor
8760
scheduled working hours(SSH)
100%
97% 85%
8463 / 6140
Scheduled operating time or Equipment available hours
6563/4390
Effective Operating Time
6366/3960
Effective Operating Time
5559/3730
2% Drop for each Belt
73% System Availability
4804/3160
G Contd. Note: In seam Mining is always practiced in flat seams while in case of steep seams Horizon mining, with its disadavntages, may have to be followed.
G Contd.
G. Main mining equipment 1)Shovel dumper technology: •
This is the most commonly used technology in Opencast mines.
•
Basically two variants – Rope shovels and Hydraulic shovels.
•
Shovel used for excavation & Dumper for transport of material.
•
Bucket capacities vary from 0.9 Cum to 40 Cum with matching Trucks/Dumpers of 16 Cum to more than 240 T.
•
Can be deployed for removal of varying thickness of materials.
•
Harder materials require blasting.
•
Can be deployed for removal of steep & thin seams (hydraulic shovels).
G. Main mining equipment
G Contd.
2)Draglines: •
A dragline bucket system consists of a large bucket which is suspended from a boom with wire ropes. • Draglines are deployed wherever there is scope for side casting overburden above coal seam into the de-coaled area. • It is very cost effective technology & can be deployed in flatter seams. 3)In pit crusher conveyor technology: • The drilled & blasted OB is loaded by shovels and transported by dumpers to Crushers. The crushed OB is then transported by a series of conveyors into a spreader for dumping. •Can be used in steep seams where laying of transport roads for the trucks is difficult. •While S.R indicates volumes,cut off ratio indicates depth and reflects in dumper haulage cost,which increase with depth and may become prohibitive where in alternative haulage system may have to thought off. •Ideally suited where material has to be transported over a large distance & lift. 4)Continuous Miner Technology:- Bucket Wheel Excavators •Presently being used in Naveyali, Lignite Opencast mines, having soft strata. •The buck wheel excavates the material without blasting which is transported by a series of belt conveyors to spreader.
G Contd.
G. Main mining equipment 5)Rock breaker technology: • •
Rock breaker technology can be applied for breaking of rock/coal/ore even about 500 kg/sq.cm. It can be used wherever it is not possible to go for blasting – near vicinity of structures and habitations. 6)Surface Miner Technology: •Used for selective mining. •Larger strike length of about 600 m – 1000 m and widths of around 300 m are ideally suited for surface miner. •Does not need drilling and blasting. The machine cuts the coal & loads into trucks for onward transportation to Surface Other common mining equipment to all the technologies •Drills •Dozers ,Graders & Compactors •Water Sprinklers •Pumps etc. •Electrical equipment •Crushers & Conveyors for Coal/OB
Rope Shovel & Dumper
Hydraulic Shovel & Dumper
An opencast mine with dragline
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IN-PIT CRUSHER CONVEYOR TECHNOLOGY (Spreader in Operation)
Surface Miner
SURFACE MINER
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Rock breaker
H. Dumping strategy and balancing Internal dumping: Depends on the steepness of the seams. As the gradient increases, the percentage of dumping reduces. Internal dumping can be increased by sectorial working of the pit – which may reduce the annual output. Toe of the dump generally kept at a distance of 100 m from the working benches. Floor of the pit to be roughened by blasting for increasing dump stability. General design of dumps: • Deck height – 30m • Berm width – 30m • Deck slope – 37½0 • Overall slope – 280 • Swell factor for OB-1.38,for coal –1.40 • Swell compact after initial settling – 1.20 Note:-Dump yard management and control is essential for the success of open cast mining. In case of more than one External Dump yards, balancing the excavation volume to either of the dump yard should be based on lead & lift and size of the Dump yards.
H Contd.
H. Dumping strategy and balancing
1.
Total dump height- 90m
2.
Deck height – 30m
3.
Berm width – 30m
4.
Deck slope-37 ½ 0
5.
Overall slope-280
H Contd.
H. Dumping strategy and balancing
1.
Total dump height- 90m
2.
Deck height – 15m
3.
Berm width – 15m
4.
Deck slope-37 ½ 0
5.
Overall slope-24.830
H Contd.
Internal Dumping reduces with the increase in the gradient of the seam.
Comparison between 1in4 and 1in8 Gradient
floor dipping at 1in8
floor dipping at 1in4 Assumptions: Strike Length Max. Depth Coal Seam thickness Annual Rated capasity
: : : :
Project Parameters Area of Excavation Mineable Reserves Total OB Removal Stripping Ratio Life of the Project Volume of Internal Dumping Volume of External Dumping % of Internal Dumping (upto Ground Level)
: : : : : : : :
1000m 110m 15m 6.0 LTPA
1in4
1in8
0.59 Sq.km 90.0 L.T 274.0 L.m3 2.74 17 Years 39.85 L.m3 234.15 L.m3 14.54
1.04 Sq.km 180.L.T 480.5 L.m3 2.67 32 Years 256.41 L.m3 134.00 L.m3 53.36
Safe distance from coal bench to toe of internal dump : 100m
50m
I. Designing the year-wise / stage – wise plans I) Stage plans • Stage plans are prepared based on Year-wise production requirements (rated out put) •
Stage plans at the end of years – 1, 2, 3, 4, 5 & in intervals of 5 years are prepared.
•
Also plans are prepared where any specific land mark like a new box-cut, change in layout will take place.
J. Financial Viability 1) 2)
The requirement of HEMM & its capital is estimated.
Other capital like developmental works, CHP etc are worked out. 3) Operating expenses are worked out to arrive at cost of production. 4) Financial viability including profit & loss , IRR etc is estimated. 5) Based on required IRR, anticipated selling price is also worked out.
L. Environment stipulations
As per EP Act 1986 “Environment” includes water, air and land and the inter-relationship which exists among and between water, air and land and human beings, other living creatures, plants, micro organism and property
L Contd.
Air
◦ Impacts: Dust is generated from drilling, blasting, excavation, crushing and transportation operations. This dust becomes air borne and gets carried away to surrounding areas. ◦ Mitigative Measures
Extensive water spray arrangements at the Coal handling sites. Wet-drilling methods are to be adopted. Water spraying on haul roads and permanent transport routes at required frequencies. Provision for mobile water sprinklers has to be made for this purpose. Extensive Green Belt development around the quarry and OB dump Black topping the transport routes and avenue plantation on these roads.
Water spraying on the haul road
Continuous water spraying on the haul road
L Contd.
Water ◦ Impacts:
Pollution of the surface water bodies with the mine discharge water and domestic sewage.
◦ Mitigative Measures:
The Mine Discharge water is to be treated in settling tanks before discharging it into the surface water bodies.
Effluent from workshop is to be treated in ETPs.
Sewerage treatment plant to be provided for treating the domestic sewage from the colony.
Impacts and Mitigative Measures
Impact
L Contd.
The main sources of noise in the project are electrical and diesel-powered machines, compressors, pumps, drilling machines, dumpers, etc. During blasting operations blast vibrations will take place.
Control Measures ◦ ◦ ◦ ◦ ◦
Controlled blasting techniques using NONELs are to be adopted . Creation of green belts of dense foliage in three rows between mine areas and residential colonies. Proper maintenance of machinery including transport vehicles. Protective devices like earplugs and earmuffs are to be provided to the needy workers. Sound and dust proof cabins are to be provided in the machines like dozers, shovels, dumpers and feeder breakers at CHP etc.
L Contd.
Over Burden Management Topsoil excavated from the quarry is to be dumped separately at predetermined place and has to be subsequently spread on external dumps for plantation.
Top soil dump is to be kept not more than 10m height.
Top soil has to be vegetated with grasses and leguminous species to maintain its fertility.
The reclamation of O.B dumps is to be done by using Biological Engineering techniques for stability of slopes and prevention of soil erosion from O.B dumps. Construction of crib structures, Gabion structures, forming of staggered Contour trenches are to be practiced for stability of slopes.
Impacts and Mitigative Measures
L Contd.
Over Burden Management
Raising of seedlings on both top and slopes of the dumps in the staggered contour trenches.
By dibbling seeds of various species like Avisa, Subabool, Babul, Neem etc.
Safe disposal of rainwater by construction of garland drains. Garland drains are to be provided around the quarry and overburden dumps .
Safe disposal of water from Top of OB
UNDERGROUND MINE PLANNING & DESIGNING
Our Technology – Under Ground Technology
• Conventional underground mining • SDL & LHD • Road Headers • Longwall • Blasting Gallery • Continuous Miners
Operational Profile • 36 UG Mines • Coal: 11.9 MT • Depths operated: 400 mts • Depths Planned: 600 Mts.
Bord & Pillar (Manual Mining) • Coal is broken by drilling and Blasting • Blasted coal is manually loaded in to tubs • Coal tubs are hauled to surface
Bord & Pillar (Semi-Mechanisation) • Coal is broken by drilling and Blasting • Blasted coal is lifted by machines and unloaded in to tubs or on to belt conveyors. • Loading Machines • SDL – Side Dump Loader (for 140 and flat gradients)
• LHD – Load Haul Dumper (for 100 and flat gradients)
SDL
Capacity : 1.0 Cu.M Avg. Production : 140 Tn/day
Capacity : 1.5 – 2.7 Cu.M
Avg. Production : 120 - 180 Tn/day
LHD
• Suitable for Thick seams around 10.0m at 100 and flat gradient. DIP
• Layout is more or less like Bord & Pillar • Development of Large rectangular pillars is done in bottom section (3.0m height) by drilling & blasting. Loading by LHD
LHD in a Blasting Gallery mine
Ring hole Blasting
• Roof coal is taken while extracting pillars by heavy blasting. • Coal from Goaf is lifted safely by remotely operated LHD. • Annual output is around 3.0 Lt
Remote LHD
TOP Gate
FACE
Direction of retreat
• Two long Roadways are driven parallel to each other by machines and connected at the end to form a Longwall face. • The long rectangular block thus created is cut in to slices by Shearer. • Coal from Longwall face is transported by series of Chain conveyors and Belt conveyors.
Bottom Gate
Road header
Supports
Shearer Face Conveyor
Continuous Miner The following mines are identified for Introduction of Continuous miners in SCCL: 1. VK –7 Incline With Shuttle/Ram cars as Backup 2. GDK-11A Incline
Continuous miner Rate of drivage –50 meters/day Production –1500 Tonnes/day For seams of 1 in 5 gradient and flatter Thickness of 3.0 m to 4.0 m
Shuttle car
Roof Bolter Bolting -240 bolts/day For seams of 1 in 5 gradient and flatter Thickness of 2.0 m to 5.0 m
Our Technology - Opencast fuelling growth…
Technology •Dragline •Shovel & Dumper •Surface Miner •Inpit crushing – Conveying – Spreading •Highwall
Operational Profile •13 OC Mines •Coal: 25.8 MT OB: 140 M Cu M •Stripping Ratio: upto 1:6 •Gradients operated : upto 18° •Depths operated: 170 Mts. The Singareni Collieries Company Limited(A Govt.400 Company) •Depths Planned: Mts.
Seams which are available at shallow depths and where stripping ratio is economically favourable Open Cast Mining is practiced Seams which are uneconimical due to high stripping ratio are mined by Under ground methods These coal seams are approached by vertical shafts and inclines Inclines are preferred when the coal seams are available at a depth of100 to 250 mts from the surface. Shafts are preferred when the coal seams occur at deeper depths
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SIDE DISCHARGE LOADER IN SEMI MECHANISATION
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Thank You
K. Coal Washing Need for Washing Power Houses consume about 75% of coal.
Power Houses are designed to accept Coal of ‘E’ Grade & above (UHV>3300). The percentage of production of coal below ‘E’ Grade is increasing .
MoEF stipulation – Presently the onus of responsibility is on end user for using Coal of not more than 34% ash if he is located over 1000Km away. Hence, the need to upgrade coals below ‘E’ Grade so as to suit the requirements of Power houses. Cost of washing is around Rs 120-130/T of raw coal.
Photograph of STP
Treatment plant for Work shop effluent
