Mining Methods• Coal is mined by two main methods - Surface or ‘opencast’ mining and 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.
Ideal conditions for Opencast Mining1. Thickness of coal seams - > 5m1. Flat gradient - < 1 in 61. Strike length - > 1 km1. No.of seams - Less the better, with higher thickness5. Coal without stone bands6. 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
General planning studies No fixed procedure – country-wise differences1. Conceptual study, data reliable upto -- 75% Review2. Pre-feasibility study - data reliable upto - 80% Additional data, modify prepare, management acceptance3. Feasibility Report/DPR - data reliable upto - 85-90%4. Detailed designing LTP/MTP - data reliability - 95%5. Operational planning (STP) - -
Basis for the initial study is Geological Report• There will be some overlap between various studies/reports.• Every step deals with Mining Technology, equipment, productionscheduling, capital cost, revenue cost, internal rate of return, dispatches etc.However the degree of accuracy of data on the above aspects increases witheach 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 (6months – one year).•These reports should adapt circular analysis approach by consideringvarious aspects like additional information available while operating the mine,slippages occurred, reserves, pit-slopes, pit-limits, pit scheduling to controlfaster rate of extraction from coal inventory which otherwise may lead toreduction in coal production in subsequent years or more equipment forhigher OB removal to maintain targeted production.
CONCEPTUAL MINE PLANNING / PRE-FEASIBILITY Deposit Tech-Aspects Economic aspectsResources Production requirementsGR/MR Mining Technology Minelife requirementsMining depth Logistics,Strata Sequa Options and Suggestions Roads etc.Thickness of- coal Cash out flow- waste Equipment Cash inflow- inter burden Required rate ofCoal Quality Surface Constraints ReturnSlope stability Cut-off SRWater Conceptual Mine Plan (Open pit layout, equipment) Modification of concept and or optimization Pre-Feasibility Study Accepted – Management Not accepted – DPR New attempt
Steps in design of OpencastA. Study of deposit exploration (GR)B. Final pit limits.C. Development sequence.D. Design of Access Ramp and Haul RoadsE. Pit designF. Annual production capacity – system availability – Mining technologyG. Main Mining Equipment – Matching to Mining PlanH. Optimizing Dumping strategy and balancingI. Year-wise / stage – wise plansJ. Financial viability (Capital & Revenue)K. Coal WashingL. 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
A. Contd. PLATES• Location Map, Top Sheet map, Roads, Lands (Forests), Rivers etc.• 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, isograde, isochore, 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)
A. Contd., Additional Data required --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 – Dewatering and depressurization hydrology - 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.
B. Final pit limits The criteria for delineation of boundaries of an Opencast Project are:Rise side boundary - Usually incrop of the bottom most seamLateral 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
B Contd.B. Final pit limits Final Pit limits Haul analysis Lead,lift increase cost – decides mode of transport Dump area 100m from mine boundary Dump limits available are Dump area 50 m from internal access road. Dump area 80-100 m. from mine infrastructure OB volumes - Final slopes Mineable Reserves – various losses, batter, barrier etc. - dilution etc (0-1 m against Roof,floor) Maximum depth increases haul cost (30-40% of total cost at 1 1/2 Km lead.Boundaries are drawn as above & Coal, OB ,SR are estimated
B. Final pit limits B Contd.Estimation of Coal, OB & Stripping ratioRough assessment is given below• Assuming Pit slopes of 450, the Quarry floor and Quarry surface are delineated• Volume of Coal & OB = Average area x Average depth - (A)• 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 = Volume of coal x Specific gravity – (C)• OB Volume = 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 Contd. B. Final pit limitsThe 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 schedulesNote:- 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. 4) Main haul road upto the pit limit should be planned in the beginning only. 5) 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. 6) 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.
D Contd.D. Design of Access Ramp & Haul roads 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 Short ramps 1 in 10 3 Lesser number of curves 4 In flat seams of haul roads can be formed over the floor of larger strike length 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 Contd.E. Pit design 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 Contd.E. Pit design 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 Contd.E. Pit design Typical High wall layout
E Contd.E. Pit design Working benches: 1) General Width - 40 – 45m Height - 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 - 60m Height of bench - 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 capacityAfter defining the boundaries, the annual production capacity will be fixedbased on the following criteria :1) The available mineable coal reserves2) Geometry of the deposit - Strike & dip rise lengths3) Structure of the deposit - 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.
F Contd.Excavator machine productivity –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 percentageProper fragmentation,less throw off material,benchheight,bench slopes ,avoiding toes and secondaryblasting,improves shovel efficiencyOptimum fragmentation-cost of drilling,blasting vis-à-vis cost of dozing,loading,hauling and dumping.
F Contd. System availability as a function of individual componentsCalendar hours-(365x24) (Figures are Indicative only) 8760 scheduled workingHolidays and bad weather 2.5%- hours(SSH) 8463 / 6140Operational delays-blasting, relocations,shiftchange,Lunch etc 1 Hour/Shift(8%)Preventive maintenance-i.e annual,weekly,daily,shift 15% of SSH Scheduled operating time orwise and unexpected break downs Availabilty- 100% Equipment available hours 6563/4390Shovel,dumper system 97% Effective Operating Time 6366/3960 12% - Crusher + 1 Conveyor 85% Effective Operating Time 5559/3730 2% Drop for each Belt 73% System Availability 4804/3160
G. Main mining equipmentFor Various Technologies 1) Shovel Dumper technology. 2) Dragline technology 3) Inpit Crusher – conveyor – spreader – technology. 4) Continuous Mining technology – Bucket wheel excavators. 5) Rock Breaker technology. 6) Surface Miner technology.
G Contd.Note: In seam Mining is always practiced in flat seams while in case ofsteep seams Horizon mining, with its disadavntages, may have to be followed.
G Contd.G. Main mining equipment1)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 toCrushers. The crushed OB is then transported by a series of conveyors into aspreader 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 dumperhaulage cost,which increase with depth and may become prohibitive where inalternative 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 Neyvali, Lignite Opencast mines, having soft strata.•The buck wheel excavates the material without blasting which is transported by aseries 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
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.Internal Dumping reduces with the increase in the gradient of the seam. Comparison between 1in4 and 1in8 Gradient floor dipping at 1in4 floor dipping at 1in8 Assumptions: Strike Length : 1000m Max. Depth : 110m Coal Seam thickness : 15m Annual Rated capasity : 6.0 LTPA Project Parameters 1in4 1in8 Area of Excavation : 0.59 Sq.km 1.04 Sq.km Mineable Reserves : 90.0 L.T 180.L.T Total OB Removal : 274.0 L.m3 480.5 L.m3 Stripping Ratio : 2.74 2.67 Life of the Project : 17 Years 32 Years Volume of Internal Dumping : 39.85 L.m3 256.41 L.m3 Volume of External Dumping : 234.15 L.m3 134.00 L.m3 % of Internal Dumping : 14.54 53.36 (upto Ground Level) 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) The requirement of HEMM & its capital is estimated. 2) 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.
K. Coal WashingNeed for WashingPower 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 forusing 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 therequirements of Power houses.Cost of washing is around Rs 120-130/T of raw coal.
L. Environment stipulationsAs 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. Impacts and Mitigative Measures• 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.
L Contd. Impacts and Mitigative Measures• 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 L Contd. Noise Pollution & Vibrations• Impact − 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.
Impacts and Mitigative Measures 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.
L Contd. Impacts and Mitigative MeasuresOver 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 .