Underground coal mining in India – Technological option and challenges ahead MD. Suresh KumarAbstractW orld coal institute estimates coal is the major contributor for energy generation to the tune of 60% and remaining from gas, diesel, nuclear, wind and hydel. In India, 75% coal is consumed by power sectors. The demand tends to outstrip domestic supply. The power sectors continue to report generation losses arfrom coal shortages. The pace of power capacity additions has hardly been commensurate with the need. Lessthan 30 GW of the planned 40 GW for 2002-07 could have been materialized as reported by The Energy andResearch Institute of India (TERI). The Government’s recent effort to build several 4000 MW power plants under umultra mega power schemes would require coal blocks with reserves of 600-700MT. The projected coal demand forthe year 2024-25 for power, steel, cement and others nearly 1147 MT which is doubled the existing coalproduction. Hence the present 6% growth in coal production would not be sufficient. hKThe country has nearly 95 BT proven and 55 BT extractable coal reserves. The coal industry in the country isgoverned by CIL 80% with 8 subsidiaries, SCCL 9% and 5% captive mines by others. As per the coal minesamendment bill, Government of India has identified captive coal blocks and nearly 291 blocks were allotted torPrivate and Public sectors to augment the coal production. But this is only transitory solution for the deficit. resBecause, most of the coal production comes from open pit mining and it nearly contributing over 84% of absoluteproduction in the country. Open pit mining has its own implications due to depth and environment pollutionwhereas billion tonnes of coal locked up in underground standing pillars and in thick seams requiring suitabletechnology. This not only shows lack of resource management but leaves a great technogical void to compensate .Suopencast coal production with proper exploitation of existing underground resources. Bulk production of coal at faster rate from underground, particularly at depth is possible from Long wall which isproven technology worldwide. Besides, nearly 40% of the proven reserves are in thick seams posing technological MDchallenge for long time. The conventional underground methods like pillar extraction and multi stage miningare only proven technologies so far in the country. The percentage of extraction in these methods is well known tobe less than 40%. The other mining methods like Wide stall, Long wall with increased height of extraction andTop coal caving are having their own draw backs. The Blasting gallery method of winning thick seams introducedin SCCL in 1989, witnessed to be great success. On the other hand, the coal pillars statued in underground both in or:CIL and SCCL due to various complex mining conditions need to be rightly exploited to the present country’scoal requirement or otherwise in-justification to the nation’s wealth. CIL has introduced short wall mining, avariant of Long wall mining to extract underground pillars. SCCL has identified few properties for short wall to thbe introduced in near future. High wall mining is the state of art of mining, gifted to the mining community worldwide to survive the open pit mines suffering from uneconomical stripping ratio. It conglomerates both Auunderground and open pit technologies being practiced in US, Australia etc., In India CIL and SCCL haveidentified coal blocks to introduce this method in coming years.This paper deals with the tale of success and failures of mining methods practiced so far in the country andexplores the possibility of sustainable winning of underground resources with the viable technological option andthe challenges ahead. Additional Manager, Underground Mech Cell, SCCL
1. IntroductionIn India, the Coal is one of the primary sources of energy, accounting for about 67% of the total energyconsumption in the country. The most of the coal production comes from open pit mines. Open pit mining has itsown implications due to depth and environment pollution. Therefore, a proper underground resource managementneeds to be explored and implemented at this juncture to bridge the technological void. Proper planning andmethodological adoption for existing underground resources only would do. The study of history of Long wallmethod in the country has not shown attractive results, but introduction of new era Long walls would break theearlier records. Enormous quantity of coal is locked up in underground standing pillars in the country. Extractionof these pillars by Short wall method and thick seam mining are the area where the Indian mining community hasto have a focus to liquidate the existing underground standing pillars. Besides, developments in exploration,detailed geo technical studies, ventilation solutions for deeper mines, hazard mapping and support techniques for arcomplex strata conditions are the pre-requisites for sustainable exploitation of existing coal resources in Indianmines. um2. Resources in Indian coal minesBeing a third coal producer in the world, India has an age old history in its coal mining sector. Coal mining in hKIndia dates back to the 18th century, however the regulatory framework for this industry was conceived in 1923.In 1972-73, the Indian government nationalised the coal industry, primarily to develop the sector, since it wasconsidered of strategic importance for rapid industrial development. India has the fourth largest reserves of coal inthe world (approx. 197 billion tonnes.). Coal India Ltd (CIL) was incorporated as a holding company for eight rescoal producing subsidiaries and SCCL is another major coal producing company in southern part of the country.Coal deposits in India occur mostly in thick seams and at shallow depths. Non-coking coal reserves aggregate172.1 billion tonnes (85 per cent) while coking coal reserves are 29.8 billion. Indian coal has high ash content (15-45%) and low calorific value. Coal in India occurs in two important types, Gondwana and Tertiary. Gondwana .Sucoal field occurs with sedimentary rock of lower Gondwana age which contributes 98% and rest is Tertiary.Gondwana coal field is distributed in the valleys of Domodar, the Son, the Mahanadi, the Godavari and Wardhawhereas the tertiary coal spreaded in extra peninsular areas. When compared to coal, the lignite reserves arerelatively modest. MD3. A look into futureIndias coal demand is expected to increase manifold within the next 5 to 10 years due to the completion of on-going coa;-based power projects, and demand from metallurgical and other industries. Demand for coal has been or:rising at an annual rate of 6 per cent since 1992-93 and CIL and its subsidiaries will be unable to meet theprojected demand alone. The investment needed to bridge the gap of 400 million tonnes, between the level ofproduction in the public sector (290 million tonnes in 1995-96) and the projected demand of 690 million tonnes th(2009-10) is estimated to be US$ 18 billion. The public sector corporations are expected to increase theirproduction by about 250 million tonnes by 2009-10, subject to their making an additional investment of US$ 8- Au10 billion. The balance requirement of 150 million tonnes will have to be met by imports in the short run and bynew investments in the long run. With the advent economic reforms, government relaxed controls on pricing anddistribution and a new coal policy permits private sector participation in commercial coal mining. Government ofIndia has identified captive coal blocks and nearly 291 blocks were allotted to private and public sectors toaugment the coal production. But this is only transitory solution for the deficit. Hence a real challenge lies on howthe existing and future underground resources are managed to produce bulk coal production.4. Underground coal mining in IndiaUnderground mining in India mainly, the room-and-pillar method with manual loading, accounts for about 20% ofcoal production. This is major limiting factor in 80s. The semi-mechanised methods using SDLs and LHDs havebecoming populous only in the last decade. Longwall retreat with caving introduced three decades ago, hasrecorded few success story due to the limitations in the method and its application in Indian conditions.
4.1. Conventional mining4.1.1. Board and pillarBoard and pillar mining is an age old mining system in the country. The development and liquidation of pillarswere manually done with basket loading onto tubs which was abundantly existing still last decade. Scraper loaderswere introduced in late 1960’s which were mounted on rails and load coal onto tubs. But it had little scope due toits limitations. Steel bolts such as point anchor bolts and wedge bolts were introduced in place of wooden supportsincreased safety and productivity. Belt conveyors replaced series of haulers and hectic tramming circuits inunderground for coal transport in 80’s.4.1.2. Wide stall methodUnder difficult geo mining conditions, where caving is restricted to protect surface features or in such conditionswhere the roof rocks difficult to cave in, the normal splitting of pillars leaving wide stook was tried but it helpedfew. Formation of stook by optimizing recovery causes reduction of strength of natural support. In such cases, thepercentage of extraction was as low as 30%. An attempt to optimise the extraction in the seams 3m plus by arheightening has weakened the pillar strength further. Under these circumstances, the wide stall method has givenbetter results. Matching of gallery size with the strength of immediate roof and strength improvement of the umnatural support by increasing width/height ratio of pillars are the two basic constituents of this method. Thestrength and size of the pillar calculated basing load expected on pillars with factor of safety atleast 2. Theeffective bearing capacity of a pillar is comparatively more than a number of stook of the equivalent area. On thebasis of extensive laboratory investigations on diffent simulated models, idea of wide stall mining was conceived hKand for the first time implemented in East Bhuggatdih Colliery of Jharia coal field. Later, SCCL adopted thismethod in Gdk-8A incline after a major roof fall accident. However, the percentage of coal recovery falls below40% and the recovery is further increased in thick seams by taking out floor coal in the mines like Gdk-8Aincline. res4.1.3. Yield pillarCoal mine bursts and sudden roof collapse are not uncommon events in most Indian underground mines understiff roof condition. However when a burst occurs, it almost results in a major hazard. Some times, the strength .Suand geometry of pillar and the rock load don’t match and may result in delayed caving, increased goaf exposurefinally its sudden failure. Besides there are number of other fundamental factors that influence such occurrence.Excess rock load causes violent failures of ribs, roof or floor. In such condition pillars shall not be furtherstrengthened to prevent caving or not be too weak to stimulate premature collapse. Over many years of dealingwith this hazard, specialised requirements for layouts and novel extraction sequences have been developed on a MDsite specific basis to safely mine coal. There have been many engineered prevention controls proposed to mitigatethe devastating effects of these dynamic and violent failures. While none of these considered as “stand alone”design, the technique of yield of pillar has come in the mind of mining engineers. A yield pillar is a pillar which iscritically-sized to withstand the abutment loads and to yield nonviolently or yield before the roof and floor sustain or:permanent damage. In India, sccl has introduced this method in one of its mines VK-7 incline to extract pillarssafely with Joy miner where the sand stone roof is reasonably hard to fall. The distressed ground conditions due tohectic depillaring done in the seam and Longwall caving in the upper seam combined with strata unconformity in ththe vicinity of faults resulting in sudden collapse of roof incurring huge loss of life and machinery in 2006 wherethis method is found more useful. However the percentage of coal recovery is not attractive due to lot of coal isleft inside the goaf in the form of pillars and stooks. Au4.2. Long wall mining4.2.1. A brief review of Longwall mining in IndiaAs a global phenomenon, the pace of technological change had been especially rapid in the second half of the lastcentury, the mechanization of unit operations led to the development of Longwall technology on the concept ofmass production in coal mining industry. It was also aimed at reducing the drudgery, monotony anddangers of work persons engaged in underground mining operations. The development of mass productiontechnology including Longwall equipment, continuous miners, ploughs and shearers have been accompanied by aseries of incremental and innovative developments in roof supporting. India also as a general rule followed theworld trend and in 1975. ‘Project Black Diamond’ envisaged introduction of 130 powered supports Longwall(PSLW) faces by the year 2000. Initially, the first fully mechanized self- advancing PSLW face was introduced inMoonidih mine in Jharia Coalfield in 1978. Subsequently more mines were planned with PSLW in the eighties,namely, East Katras ( BCCL), Seetalpur, Dhemo-Main, Jhanjra, Khottadih (all in ECL ),Patharkhera (WCL) andChurcha (SECL), and first long wall in SCCL introduced at GDK 7 incline in 1983 at also a few other mines in
Company. In the process about 30 PSLW sets had been imported from different sources in different countries like,UK, Poland, Russia, Germany, France and China. Barring a few exceptions, where the powered support Longwallfaces gained moderate success. Most of the Longwall faces were far from the desired level of production andproductivity on sustainable basis. Further large scale introduction of Longwall technology received severesetbacks due to its successive failures at Churcha (SECL) and Khottadih (ECL) mines. At present, Longwallmining accounts for a meager production of about 4% of the total underground production4.2.2. Factors affecting the Longwall performance in Indian mines188.8.131.52. No Policy for Introduction of Mass-Production TechnologyEven after nationalization, the Govt of India was not firm on policy for mass production technology, likeLongwall and continuous miners. Because of that no private/government company has come forward formanufacture of underground mining equipments for mass production technology.184.108.40.206. Standardisatin of Longwall equipment arThere was no standardization of Longwall equipment in the country. As such, different Longwall equipmentpurchased in India are of different specifications. As a result, no indigenous manufacturers were motivated to ummanufacture small demand of Longwall spare parts. Delay in procurement of spares affected production fromLongwall panels. As the number of operating faces are less, the suppliers were not able to provide eithermanufacturing facilities or spares depot within India.220.127.116.11. Wrong place of Application hKThe study of few cases in the country revealed that the Longwall technology was introduced in extremely criticalconditions such as difficult geo-mining conditions, steep and thin seams, at deeper horizons with very highambient temperature, Degree-III gassiness and mine where coal evacuation system was extremely circuitous witha series of conveyors. These factors proved a serious bottleneck in improving productivity from Longwall faces atits very budding stage and gave a wrong signal as if the techno-logy is not suitable in Indian mining conditions. res18.104.22.168. Face geometryLongwall face width was designed from 60m-165m, the length varying between 500m to 1.2Km and operated indepth 30m to 350m so far. In these conditions, very few mines recorded good results such as VK-7 and Gdk-10A .Sumines of SCCL with regard to consistency. Non-availability of longer panels due to geological disturbances, ordue to surface features to be protected and presence of standing pillars in an upper seam yet to be extracted,resulted in frequent shifting of equipment and increase in non-productive work and time. Whereas the coal seamsextremely favoured Chinese, Australian and US mining industries to have longer and wider panels.22.214.171.124. Lack of Infrastructure Facility MDIntroduction of Longwalls in already existing mines which were not having sufficient infrastructure to match thedesired level of production resulting in derating the projects. Provision of matching infrastructure was eitherdelayed or never came up in most of the cases.126.96.36.199. Advanced geo-technical studies and R&D facility or:In most of the cases, inadequate geological information and geo technical knowledge due weak borehole densityto become major chunk for failure which is often led to wrong planning including those wrong selection of powerroof supports, orientation of panels with respect to horizontal stress direction. Further it led to too manygeological surprises while working the face. The weak geo-informations resulted in wrong projections of faults, ththinning of seams, intrusions and variation in strength of immediate roof rocks. The poor knowledge of hydro-geology drawn the faces and continuous water percolation in the strata led to strata control problems in many Auincidents. The most glaring example in this regard is failure of powered supports at Churcha (SECL) andKhottadih (ECL). In both the cases the supports collapsed and failed to withstand the load exerted bysuperincumbent strata during periodic weighting due to underrated supports. These two incidents gave severe joltto the programme of large scale introduction of Longwall technology in other Indian mines.188.8.131.52. Technical lapsesThere used to be some severe technical lapses pertaining to face operations that the development with olderversion Road headers like AM-50s and Doscos are not matching with Longwall retreat rate, LW units wereintroduced inferior quality top and upper seams which hugely affected economics, Lack of man riding facilities inunderground leads workmen reaching to face getting delayed and interrupted face operation too and theconventional face transfer system including equipment withdrawal from one face, transporting to another face andinstallation in the new face consumed 3 months to 6months.
4.3. Extracting thick seams4.3.1. Blasting GalleryThe Blasting gallery method of thick seam extraction was introduced in SCCL during 1989 with the technicalcollaboration of Carbonages de France (CdF), France. Based on its success, the method was introduced in fivemines of the company in VK-7, 21incline, Gdk 10incline, Gdk 8 incline and Gdk 11A in phases in the last twodecades. Over this period, the Blasting gallery method is established as an economically viable with a source forbulk production. Evidently, this method is so proved to be safer due to its inherent mechanisation of drilling,loading, transporting and supporting. The bottom section of virgin coal seam is developed in series of headings at22-25 interval called ‘Rooms’ and connected 80-120m apart to form sub-panels. Such set of sub-panels rangingfrom 4 -7 formed a Blasting Gallery panel. A first roof blast called ‘potato blast’ is done upto to the full seamheight at the in-bye end which creates free face for further blast holes. Thus the rooms are retreated continuing theblasting upto full seam height following a diagonal line. A mobile electric drill drills shotholes all around theroom, at an angle inclined towards goaf upto full seam height in a ‘Ring pattern’. A ring contains 22-35 holes as arper the requirements. The different operations like drilling, blasting, supporting and coal production would gosimultaneously in the different rooms. Therefore an average production of 1000Te could be achieved from a umpanel. Whereas the percentage of coal recovery would be higher than the any other methods exist presently. In thelater stage, it was focused to adopt the same methodology to extract coal from developed bord and pillars. Panelswere formed by constructing isolation stoppings around and the Rooms were formed by splitting the existingpillars. As the mines having intensive development in standing pillars, this method fed right stuff to the minerswherever technically applicable.4.3.2. Multi-stage mining and Stowing hKBefore the Blasting gallery was landed in Indian soil, thick seams in the country mostly were developed in two orthree lifts depending upon the seam thickness leaving minimum of 3m parting between the lifts as per the resstatutory requirement. Such seams were developed with room and pillars superimposed. Conceptually, this hasgiven confidence amongst the mining engineers with regard to percentage of recovery of coal seams. Later thebottom section coal was extracted with stowing then the top section coal was removed with or without leaving .Supartition.4.4. Introduction of SDLs and LHDsSDLs and LHDs were introduced only in the last decade in the country. It simply replaced manual loading in theconventional face. A review of accidents where the face workmen involved has thrown serious thoughts of MDmechanisation of manual loading. It was taken almost a decade to eradicate manual loading in phased manner.Initially Eimmco Elecon SDLs and 811 LHDs were introduced in the mines without much concentration onapplication techniques in relation to the mining conditions. Later, on care full studies with field experience correctapplication was chosen with respect to seam height, gradient, floor conditions and water percolation. Further or:improvement was achieved by introducing Simplex SDLs and higher capacity E-912LHDs in the later part of thedecade. However, the introduction of this intermediate technology not only replaced manual mining but reducedhuman drudgery and improved safety & productivity. th4.5. Continuous minersAs the cost of production and accidents trend are on higher side in mines operated with manual loading led to the Authought of introduction of CM technology. The first fully mechanised room and pillar system in India, usingcontinuous miner technology, started its operations in May 2002 at Chirimiri Anjun Hill Mine, South EasternCoalfields Limited (SECL) on risk/gain approach.. The complete system, supplied by Joy Mining Machinery Ltd,included a 12CM15 continuous miner, two shuttle cars, a feeder breaker, a mobile roof bolting machine andelectrical distribution system. Since start up, the system has averaged over 40,000 tonnes per month on thedevelopment of a five entry room and pillar system and has now achieved over 50,000 tonnes in a month on de-pillaring. To date the de-pillaring operations have been very successful providing the only approved method ofmechanised de-pillaring in India. In the present technological transformation, with considerable awareness andtraining it is possible to produce 4 to 6 LTPA in Indian mining condition. Presently miners belong to JOY andDBT are working in Anjana Hill Mine, Chirimiri (SECL) commissioned in May 2002, Thandasi Mine (WCL)commissioned in June 2003, VK No: 7 Incline, Kothagudem (SCCL) commissioned in Aug, 2006. JhangraUnder ground Mine (ECL) commissioned in June, 2007 and GDK 11A Incline (SCCL) commissioned in Dec,2008.
4.6. Short wall miningThe shortwall mining technique is similar to longwall mining but with shorter face lengths, ranging between 40and 90 m, with the aim of controlling the caving nature of the overlying upper strata, the load on support and theoverall operation of the supports at the face. Though the concept of shortwall initially aimed at this, Chinesemines have introduced this technology to mine out standing pillars. The similar equipment used in Longwall isutilised here too and open galleries ahead the face are well supported with longer roof bolts and cable bolts.Additionally, breaker line supports which are of normal power supports set in the open galleries with remoteoperation. Self advancing, crawler mounted supports are also used as breaker line supports. As per Indo-Chineseagreement, the first shortwall was introduced at Balarampur of SECL where three such short panels have beensuccessfully completed and SCCL too planned to introduce shortwall in one of its mine RK-NT. The success ofthis method in this two coal companies may lead the entire mining industry in the country to a newer thinking toliquidate its vast standing on pillars property. ar5. Road map to Indian coal mines for sustainable exploitation5.1. Exploration and detailed geo-technical studies umRecently, SCCL has entered into MoU with CSIRO, Australia for implementation of first ever high capacityLongwall technology where the detailed studies have been conducted which broadly includes increase in boreholedensity to 20 / Sq Km, study of overlying strata behavior upto the height of 100 to 150m over the Longwallpanels. The existing practice of study levels depends on the requirements of the projects. Complete and detailed hKstudies of entire block are not done before implementing the new projects like in US and Australian practice.Besides, in the most of cases the mining projections are made depending on the existing geological data. As far aspracticable, coring needs to be done for each borehole, preserved in core library for analysis and photographedtoo. The data from non cored boreholes can be generated with Geo–physical logging (neutron, gamma, resistivity resand density. In-situ stress and permeability measurements must be conducted in the boreholes equally spreadedover the proposed panels. The permeability tests shall be conducted in different depth horizons to have mostrepresenting result ranging from barren measure rock upto geological domain rocks including inter burden. Apartfrom the above, PMP tests, Caving index, In-situ strength of coal, Piezometric studies core profiler and micro .Sulogging shall be done to formulate most realistic mine panning. Minex modeling is the one software launched inIndia and found its success to delineate the coal/ore structure.5.2. Making Longwall Technology successful MD5.2.1. Things to be learned from ChinaChina introduced Longwall mining in the late seventies and early eighties as in India, but within 20 years it hasnot only emerged as the world leader in coal production, but has established itself as the largest user of Longwalltechnology in underground mines and has created for itself an international market for export of the technology,expertise and equipment. From the very beginning, it adopted wholesome approach for large scale Longwall or:mechanisation in their UG mines. Their approach was very methodical and it took into account their own socialand economical conditions. Instead of instantaneously jumping into hi-tech mechanisation only in some isolatedmines, they introduced the technology stage by stage with incremental development. China has developed tailor thmade equipments suitable to their conditions. For this they have first generated skilled workforce of Engineers,operators, designers, research institute personnel and manufactures. They gave greater emphasis on applied R & Dfor product design and quality development. China has developed huge infrastructure at unit levels as well as Aucentral levels. It has constructed a number of new highly productive and efficient mines with different capacitiesbased on seam/geological conditions by identifying suitable coal blocks in advance. It has improved itsmetallurgy for indigenous manufacture of powered supports with higher support resistance, more powerfulshearer, AFC and belt conveyor and started achieving 6-10mt coal from a Longwall face per annum.5.2.2. Suitable blocks for wide and Lengthy Longwall facesIt is extremely important to choose the proper place of application of this mechanized Longwall technology,which is capital intensive and involves a lot of time and manpower in installation, salvaging and shifting ofequipment. As the existing underground mines in CIL and SCCL have got limited scope for this technology as foras the infrastructure is concerned. Hence, suitable virgin blocks can be sought for. As far as practicable, no othertechnology shall be combined with Longwall. The expansion of existing mines is possible but only beyond 300mdepth where it is required to explore success of Longwall face at deeper horizons. The existing facilities like manriding, ventilation and coal conveyance can be utilised during development till permanent set is made. The
minimum proved resources should be 100Mte so that the projects can be sustained for 25-30 years with oneparticular set up or infrastructure. Today the world trend is to provide longer and wider panels to minimize thenumber of shifting.5.2.3. Proper equipment for specific geo-mining conditionsIt is required to do advanced studies, numerical modeling and preparation of adequate of data related to thespecific geo-mining conditions of the mine, to make Longwall equipment tailor made to the site specific geo-mining conditions. More over, one set of equipment can be used with only minimum modifications. Moreparticularly, the power supports which are available in varieties in the market shall be carefully selected withrespect to their load resistance, load expected from overlying strata and seam gradient.5.2.4. Indigenous capacity of equipment manufacturing at Low costThe private parties entering into Longwall equipment manufacturing and its spares is mearly nightmare except arfinger count. But it may take another 10 years to develop the vendors to get technical expertise. With the mixedresult of Longwalls in the last 30 years, the Economy of the projects did not bring any fruitful results mainly due umto the landing cost of the equipment. Two important reasons can be attributed that the number of operating facesand equipment cost. Developing country like India was not in a position to bare any economic fall outs due tofaces failed to produce to its rated capacity. Success not to come easily on its way, but out of sustained and hardeffort. Sufficient effort was put all these days and Longwalls in the country have produced a huge number of hKexperienced mining engineers and experts. But the ultimate requirement is, to reduce equipment cost andoperating cost with self manufactured indigenous technology.5.2.5. Both CIL and SCCL have to launch LW technologyThe indigenous technological expertise comes only if much more Longwalls, atleast 30-50nos with range of face reslengths are both in SCCL and CIL having at least 25 years of project life. The most of the coal seams in thenorthern part of the country occurred at lower depth with stripping ratio as low as 0.5 which neither posed anycoal scarcity nor warranted underground large scale mechanisation in the last 30 years. But the situation is .Suupturned now and it is bound to makeup the coal demand from underground mines. The Central Government andits planning commission assessed the ground situation and taken proactive decision to decentralise the mining byopened up nearly 300 blocks given to private parties for capital coal utilisation. Experts anticipate only mixedresults out of this. A real improvement and next generation mining can be achieved only if CIL which is a largermining operator in the country comes forward to do Longwalls for mass underground production. MD5.2.6. Introduction of High capacity Longwall for the first time in the country-scclHaving understood the need of sustained underground mining, The SCCL has timely planned to introduce a latestversion Longwall face on par with USA, Australia and Chinese mines. Around $160 million worth first ever high or:capacity Longwall Project of which the equipment is supplied by BUCYRUS. The production capacity would be3Mtpa with panels ranging from 1500 to 2500 m length, 250m wide faces, Depth of working upto 600 m, Seaminclination 1 in 5 and height of extraction is 3m. The supports are 1152 Te 2 legged DTDA shields with 120/104tpsm support density, the shearer type-EL3000 with all electrical motors includes 2x860kw cutting motors, th3000tph cutting speed and 0.85m web, 3x855kw twin inboard AFC, 400kw BSL, 1600mm 3200tph gate belt withother high capacity back up arrangements. For the first time in coal mines in the country a deep shaft 468m is Aubeing sunk for ventilation. More advanced from conventional like shifting of power packs and electricals withmonorail system and FSVs for transport of supports, men and materials. The entire country is looking forward tosee its implementation and success of this project which may give solution for implementation several highcapacity Longwalls in future.5.2.7. Bolter miners for Roadway developmentThe one of the reasons that the Longwalls in the country is barking down is the panel’s development rates. Thelow capacity Alpine miners and Doscos are used for panel development whereas machines were modified to theirneeds in US, Australia and in China. High powered cutter motors, robust cutter head and traction system in latestversion machines improves machine stability, ability to work in seam gradients upto 10-150 and faster drivage.The on-board bolting facility further improves machine utility hours and proved the development rate 400-500 permonth. However, Continuous miners had been dominant in development with twin gate roadways two decadesago. Miners with on-board bolting facility and Bolter miners have further boosted the rate of drivages to cop-up
much sophisticated 6-10 Mte producing Longwall faces. Thus bulk output from Longwall face can not beachieved without bolting facilitated miners or Bolter miners. There are verities of machines available in themarket to choose the best fit to seam and mining conditions and economy.5.3. Liquidation of existing standing pillars5.3.1. More short walls in futureReintroduction of Long walls is emerging with new strength and high expectations both in CIL and SCCL. Hence,introduction of more shortwalls may be delayed as it needs combination of older equipment and few newadditions. As such, shortwall sets, if purchased, may not justify economics with low range of production. Duringfirst phase of its introduction, it is possible to put them in existing or older Longwall facilitated mines havingenough infrastructures. More new faces with infrastructure is possible in future with indigenous equipment.5.3.2. Continuous miners arLiquidation of standing pillars with intermediate technologies like SDLs and LHDs with caving or stowing havegot its limitations due to scarcity of timber and sand near the mining areas. Face drilling for blasting and bolting isa big concern as done mostly manually, consumes lot of time and reduces machine utilization. Mechanised drill ummachines like pneumatic drills, hydraulic drills and UDMs were introduced but did not prove as triumphantmatching machine. This is the reason, they produce just above the break even production and in many mines theyproduce less than that. Venturing for bulk production is unattainable with these machines even with morenumbers. The only solution left with is miners. The present miners in India, except Chirimiri and Tansi, reported hKaverage performance. More experience, expertise and planning would make turn around. There is range of productavailable in the market to suit to the mining conditions. But the concern is landing cost of equipment imported.However it is not far from the reach that indigenous miners at low price may be dominate the market in thecoming years. res5.4. High wall mining for deep seated OC propertyHighwall mining is extracting coal from the face in a seam exposed in the final bench of opencast mine, afterreaching to its economical stripping ratio. The extent of an opencast mining is limited by the financial viability, .Suthough coal seam continues to exist beyond the quarriable limits. Irrecoverable coal is lost forever within thehighwall. Thus, highwall mining is a valued technology which can revolutionise maximization of extractablereserves. This technology is being practiced in USA, Australia, and Indonesia and is likely to be introduced inIndia in Eastern Coalfields Limited and Tata Steel – West Bokaro in coming years. CIL has identified 17 mines MDsuitable for highwall mining and SCCL 6 blocks. Coal is extracted with miner or borer and coal is transportedwith belt or piped conveyor without artificial roof support and ventilation. The cars are added one by one behindthe miner as it cuts in the seam, in a manner which does not interrupt the flow of coal. The launch vehicle is a twodeck steel structure which sits on the floor of the pit at the base of the highwall. It serves as a work platform,propulsion unit and utilities supply center. It remains stationary during the mining process, providing a stable or:anchor point for the equipment at the highwall. It contains an electric power distribution center, a control cabinfrom where the operator operates the entire system by remote control, two separate hydraulic power systems, aswell as cable and hose reels for electric power, coaxial cable and water. th Fig: 1. Typical components of a Highwall Mining Equipment AuAs this method involves drivage of series of parallel roadways into the highwall along a particular horizonseparated by ribs, the dimensions of the roadway, the thickness of the ribs, the maximum depth to be operated
depends on the geo-technical characteristics of the seams / strata and surface features. Since the Technology isnewer to India, all these parameters should be carefully studied before implementation.5.5. Ventilation for deeper coal mines and introduction of air cooling system in undergroundThe first shaft for coal mine, only 27m deep was sunk in the year 1851 at Eagra near Damalia in Raniganj coalfield. Whereas a number of shafts of greater than 1000m depth were sunk in 1890s and 1910s at Champion reef-gold mine in KGF reached to a depth 3211m which is one of the deepest mine in the world. Whereas, the coalmining operations have crossed 300m depth and extending beyond 400m in the country and facing complexclimatic conditions with high dry bulb temperatures due to strata temperature, mechanisation and humidity.Hence, it is a need of hour to formulate efficient ventilation in underground to create comfortable conditions.Deep shafts are inevitable to bring cool air at the deep most points. Higher capacity fans upto 400m3/minoperating upto 250mm water gauge are to be planned to work mechanised faces in deep seated reserves. Except infew metalliferrous mines, air cooling/ refrigeration was not practiced in coal mines so far. But the present arsituation emerges underground cooling system to reduce ambient temperature of intake air. SCCL is installing itsfirst refrigeration plant in underground 500TR chiller with 45000CMH air handling unit working at 40 mm water umgauge at Vk-7 Joy miner face and planning to install in two more mines. CIL too planning to introduce AC plantsin underground. The cost of refrigeration per tone of coal against the losses that made out of inefficient ventilationis highly insignificant.5.6. Thick seam mining hKA huge amount of coal reserves is being locked up in thick seams in the country. Both CIL and SCCL havinghuge amount of reserves of such kind. The conventional underground method of board and pillar development anddepillaring in multistage with or without stowing is only available and proven technology exists all these days.The percentage of extraction in this method is well known to be less than 40%. The other mining methods like reswide stall, sub levels caving, Longwall with increased height if extraction and Longwall with top coal caving arehaving its own drawbacks due to either less percentage of extraction or newer technology which is not yetpracticed in the country. The SCCL itself is having thick seam reserves about 40% out of two thousand million .Sutones of proved coal. Interestingly, Australia too has huge thick seam coal resources. The coal reserves in thickseams in both countries aggregate to several tens of billion tonnes. The current mining methods and designs forthick coal seams in underground mines are inefficient and result in huge losses of valuable coal resources in bothcountries. A MoU was signed by India (SCCL) and Australia (CSIRO) jointly with the major outcome ofoptimising extraction methods and/or designs to substantially improve recovery rates and safety of mining MDoperations in Indian thick seam environments.5.6.1. Blasting gallery- a success venture in SCCLThough this method was seemed to be conceptually easier and operationally dangerous in initial days, the simple or:mechanisation and the face operation without much complication are the key factors that made people to be wellconversant to the applicability of the system with respect to their local mining conditions. A hydraulic supportswith canopy specially designed for the purpose of having allowance to LHDs to ply can replace existing manual thinstallation of steel bars supported on OC props. Walking breaker line supports in the junctions could reducehuman drudgery and still safer and productive too. Au184.108.40.206. Strata control problemsThe experience in SCCL reveals that caving is not a problem in the coal seams with overlying strata havingcompressive strength varying between 100-300 Kg/cm2 and of easy to moderate caving roof. The technique ofinduced blasting incorporated in this method had proved to be given better results in bringing down the immediateroof at desirable interval. The regular falls of immediate 3-5m layers of overlying sand stone strata allows theupper and massive layers to readily cave in. Every periodic fall and induced fall posed minimum impact on thegallery supports and roof and sides. While working over the worked out panels of bottom seam and simultaneousworking of lower and upper seam in gdk-8 incline revealed that the insitu stress domine is reasonably damaged tofavour easy caving.220.127.116.11. Fire control in BGsSpontaneous heating is one of the major problems being faced here. The occurrences of spontaneous heating inworking panels, not only threat to the general safety, but it forces to close down the panels losing huge quantity of
natural resources. It often ended up in sealing a large section of mine affecting the mine economics adversely.Therefore the prevention of spontaneous heating in Basting gallery become inevitable for mining engineersotherwise working of thick seams become questionable. The BG panels are being successfully mined in SCCLwith the following preventive measures:1. Monitoring in-bye most goaf atmosphere through pipelines, thermal images camera and surface boreholes.2. Removing floor coal and curtain coal meticulously during extraction and descenstional ventilation system to contain the gases inside the goaf and to restrict goaf ventilation.3. Regular induced blasting at an interval of 5m and up to 9 to 10m height in roof to reduce strata control problem as well as fill the goaf regularly avoiding air pockets inside.4. Proactive inertisation by continuous injection of CO2 and N2 into active goaf. A storage tanker with a capacity of 30 metric tones of liquid CO2 ensures its constant availability through pipe lines. Combination CO2 and N2 creates identical density of goaf gases which advantageous that they can cover up the entire sealed off area in a quicker period. CO2 has an added advantage that it reacts endothermally consuming heat of 40.8 kcal/mole of ar CO2. CO2 is always better in quick replenishment of air, being heavier than air. Besides N2 creates congenial environment particularly when liquid N2 is used. um5. Inertising the adjacent sealed off panels too. Fig 2: Surface CO2 Storage tank establishment at Gdk 10A mine. SCCL. hK res .Su5.6.2. Long wall top coal caving-LTCC MDThe LTCC method is based on the Soutirage Longwall caving method originally developed in the French coalmining industry. Then Australia and China have started LTCC for thick seam mining. It basically involves anadditional AFC to transport top coal falls behind the Shields. When compared to other thick seam miningtechniques it ensures a high recovery rate and productivity. However, it is reported that 24 % of the coal reserve of or:a panel operating by LTCC is left behind the face. But today, with the experience of support operators; the coalrecovery percentage is increasing year by year. As an equipment innovation, the more recent Chinesedevelopments have relocated the top coal draw points to the rear of the longwall supports, rather than bringing thcoal through the roof canopy of the shield onto a conveyor within the shield structure. The Chinese equipment hasa pivoting supplementary goaf or tail canopy behind the support. With the rear AFC extended and the rear canopy Aulowered/retracted, caved top coal can be loaded onto the rear AFC. The Chinese industry had reported averages of15,000 to 20,000 tpd from an LTCC face; up to 75% recovery of plus 8m thick seams using a 3m operating heightlongwall and plus 5 MTPA face production. There are now well over 70 LTCC faces in China. A new semi-automated 300m long LTCC face was installed at the Xinglongzhuang Colliery of the Yankuang Group, inShandong Province, in August, 2001, with production capacities of at least 7MTPA. The consistent cavability ofthe top coal in an LTCC operation is crucial to its success. If the coal caves, but in too large a pieces it can causeblockages and handling problems both feeding onto, and traveling along the rear conveyor. Of even greaterproblem is if the coal hangs up, even only for a short time, such that it caves but beyond the reach of the rearAFC. The main geotechnical components affecting coal cavability are uniaxial compressive strength (UCS);cleat, bedding and other discontinuities; and vertical stress on the coal. Chinese experience is understood to bethat compressive strength ranging from 15 MPa to 25 MPa is well suited to good caving conditions. Horizontalstress too has lot of influence.
6. ConclusionIndia, being a third coal producer in the world and producing nearly 85% of coal from opencast mining presently.The country has to exercise lot to get bulk output from underground mines. As the opencast mining have its ownimplications due to depth and environment pollution, bulk production is possible by opening new coal blockssuitable for sophisticated mechanisation and managing existing coal resources in underground mines to achievesustaining improvements. Country need to focus Longwall mining and ought to revive its earlier policy 1975‘block diamond’ to introduce power supports Longwall in both CIL and SCCL in feasible blocks having goodquality of coal. If Longwall faces planned abundantly, it creates a base for competition in foreign manufacturersand develops indigenous market too which would bring down cost of production. Different modules like minedeveloper cum operator (MDO), Technology provider cum operator (TPO) and Risk/gain sharing can be workedout with foreign participants.Blasting gallery is typical mining method to extract thick seams presently. The method is moderately mechanised,not much complicated and proved to be safer in operations in the last two decades in SCCL which is to be arpractised elsewhere in the country with further safety and productivity inputs. The number of CM units, presently5 in the country should be multifolded to develop and extract 3-4m high seams. Shortwall mining a variant of umLongwall to extract standing pillars presently practised in SECL mines and proposed in SCCL too, must be vastlyimplemented to all the feasible mines. Highwall mining is a state art of mining by which the huge quantity of coalis locked up in highwalls of opencast mines can be successfully mined out.References/ Literatures1.2. hK US Energy Information Administration – independent statistics and analysis 2009. Report on 4th Thermal power India 20103. Report on “competition in India Energy sector” by The Energy and Resources Institute (TERI). res4. Report on “The Expert committee on road map for coal sectors reforms” by Ministry of Coal. GOI. April 20075. Report of the working group on Coal & Lignite for formulation of Eleventh Five Year Plan (2007-12) by GOI, Ministry of Coal, Nov 2006. .Su6. A Report on coal industry by “The Director, Coal Controller’s Organisation , Kolkatta.7. Application of Nitrogen as preventive and controlling surface fire – Indian context by NK. Mohalik, RVK singh, J. Pandey and VK singh. CMRI. 20058. CMRI S&T report, study for early detection of the occurrences of spontaneous heating in the Blasting Gallery MD method and to evaluate suitable measures for prevention and control (CMRI-2002).9. Why Longwall in India has not Succeeded as in other Developing Country Like China by Prof A K Ghose, Fellow10. Why Longwall in India has not Succeeded as in other Developing Country Like China by S R Mehta, Non- member S Dasgupta, Non-member or:11. Longwall Mining in India – Experiences and expectations by Sri DLR Prasad (Director PP) and M.S. Venkataramaiah (AGM).12. Hamilton N, (1999) Single pass thick seam Longwall experience at West Wilsend Colliery, second th International Underground coal Conference, UNSW, Sydney, Australia 15-18 June,1999 PP55-61.13. Hebblewhite BK &Cai YI(2004) evaluation of the application of the Long wall Top Coal Caving (LTCC) method in Australia, UNSW Mining Research Center, School of Mining Engineer, Sydney, Australia. Au14. Peng SS. Chiang HS (1984) Longwall Mining, John Wiley & Sons Inc, PP 274-333.15. Singh R, & Singh TN(1999) Investigation into the behavior of a support system and Roof strata, Geotechnical and Geological Engineering 21-35. Netherlands.16. Walkers, Highwall evaluation World Coal Vol. 6 No. 10 Oct. 1997 PP 44-52.17. Analysis of Practical Ground Control issues in Highwall Mining by R. Karl Zipf Jr. & Suresh Bhatt. National Institute of Occupational Safety and Health Pittsburgh. Pennsylvania. USA.18. Superior Highwall Miners. LP. Beckley, West Virginea. http:www.shm.net.200419. Mining technology Inc, Ashland, Kentucky, http:www.addcarsystem.com. 200420. Duncan-Fama, ME Shen B, Craig MS, Kelly M, Follington IL and Leisemann BE Layout and Design- Case study for Highwall Mining of coal. Proceedings International Congress of Rock Mechanics eds. G.Vouille and P. Berest 1999 vol 1 pp 265-268.21. High wall mining in Australia by left Sartaine. President, Mining Technologies. Inc.22. Report on introduction of Shortwall mining in SCCL by CODCO, China, 25 Sep. 2009.