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Longwall technology in india, SCCL


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longwall experience in SCCL india

introduction of longwall technology in India, comparision of longwall performance with China and measures for improvement, success in implementation of longwall technology

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Longwall technology in india, SCCL

  1. 1. 3rd Asian Mining Congress 22 - 25 January 2010, Kolkata, India The Mining, Geological and Metallurgical Institute of India (MGMI) A RETROSPECTIVE ASSESSSMENT OF LONGWALL MINING WITH A FOCUS ON SUCCESSFUL MECHANISED UNDERGROUND MINING TECHNOLOGY V. N. S. Prasad1 , M. U. Siva Sankar2 , Prof. S. K. Mukhopadhyay3 and Prof. Debasis Deb4 ABSTRACT The global demand for energy continues to grow at a rapid pace, driven by both developed and developing countries. Coal has major role to play in meeting this demand and it must be ensured that it remains available and competitive with other energy sources. Coal occupies the centre-stage in the energy economy of both China and India; coal has a share of more than 70% of the primary consumption of energy in the current mix of commercial energy. Under ground mined coal accounts for more than 50% of total global hard coal production and in China, 95% of hard coal production comes from underground mining. Surface mined coal alone can not meet the huge growth in demand that is forecast for India. Some import of coal will be necessary, the amount dependent on how successful the Indian underground coal industry is in stepping up to the challenge. In order to keep pace with the growing Indian economy at the rate of 8 to 9%, the coal industry requires narrowing down the supply-demand gap at a competitive price. Mechanised Longwall mining is a sustainable option to achieve higher production and productivity. This paper looks at the retrospective assessment of production performance and short comings for under rated performance of Longwalls in India, particularly of Singareni Collieries Company Ltd (SCCL), in comparison with other countries especially China. The authors also expressed thrust areas to be addressed for successful implementation of Indian Longwall mining to meet the global standards. Keywords : Longwall; SCCL 1 M.Tech Student IIT Kharagpur, Under Manager, SCCL, 2 M.Tech, Under Manager, SCCL, Kothagudem – 507101, A.P. India e-mail: 3 Professor, Department of Mining Engineering, IIT Kharagpur – 721302, 4 Associate Professor, Department of Mining Engineering, IIT Kharagpur – 721302, INTRODUCTION India has vast natural resources with the world’s fifth largest coal reserves. The depth wise coal reserves of India as on January 2005 are as given in Table 1. At present rates of growth it will soon be the world’s third largest coal producer. It is worth noting that India is also presently the world’s fifth largest importer of coal, and unless major steps are taken the amount of imported coal will need to grow drastically1 . Total annual hard coal production in India is about 450 Million tonnes (Mt), out of which nearly 83% is from opencast mines. At present percentage of contribution to the underground mining
  2. 2. 160 A Retrospective Assesssment of Longwall Mining With A Focus on Successful Mechanised Underground Mining Technology production by mechanized Longwall mining in India is less than 4%. The expected demand for coal by 2011-12 is about 707 Mt; where as coal production would be around 550 Mt, leaving a gap of about 157 Mt, which needs to be met by imports or private mining2 . The production from underground coal sector has remained practically stagnant for the last three decades. The technological up gradation in underground mining methods in India during this period was very marginal due to inadequate investment and lack of any serious approach for its development. To cope up with the fast growing demand of coal, entire attention was given to the comparatively easily available option of opencast mining which proved to be more productive and economical. With economic liberalization and consequent reduction of import duty on coal, the coal mining industry in India is facing a new challenge and India can no longer rely on opencast mining alone. For bulk production of coal at faster rate from underground coal mining particularly at depth the proven technology world over is Longwall. Table 1 : Coal reserves in India Depth(m) Proved Indicated Inferred Total (in Bt) (%) 0-300 71 66.5 15 152.5 61.5 300-600 6.5 39.5 17 63 25 0-600(Jharia) 14 0.5 - 14.5 6 600-1200 1.5 10.5 6 18 7.5 0-1200 93 117 38 248 100 (Source: GSI Report, Jan’2005) (Bt: Billion tonnes) GENESIS AND EVOLUTION OF LONGWALL TECHNOLOGY The seventeenth century innovation of ‘Longwall’ system in Shropshire in England has made giant strides over the past three centuries to emerge as the predominant bulk production system in global coal industry today with a share of nearly 70% of aggregate production and is recognized as the safest, the most productive and cost effective method as well as for extraction of coal seams by underground mining3 . In India first mechanized powered roof support (PRS) face, the new-age Longwall, was launched in August 1978 at Moonidih Colliery4 . In India, 33 Longwall packages have been deployed to date in Coal India Ltd (CIL) and Singareni Collieries Company Ltd (SCCL) in collaboration with U.K, Russia, China, France mostly funded by GOI. During these three and half decades of Longwall experience powered roof supports of capacity varying from 280 to 800 tonnes have been used at many mines in India under varying geo-mining conditions5 . Majority of the Longwall faces in India have been worked under relatively shallow cover (< 200m) and significant problems on the cavability of the roof have been experienced6 . The overall performance has fallen short of expectations despite the above experiences. Only a few of the faces could yield planned production level for initial three to four years of support life. A number of reasons have been attributed to the lower performance of such Longwall operations6 - 9 . Severe strata control problems at face resulting in damage of supports and increased downtime of equipments substantiated by improper matching of the sub systems are understood to be two prime reasons for such poor performance. An unsuitable locale selection incompatible with the selected supports due to improper pre-investigation studies while planning worsened the situation in few cases. In China, first fully mechanized face using chock type supports was introduced at Meiyukou colliery in 1963.
  3. 3. V. N. S. Prasad, M. U. Siva Sankar, Prof. S. K. Mukhopadhyay and Prof. Debasis Deb 161 Since then introduction of fully mechanized faces in coal fields of China have been a classic case of large-scale diffusion, using both imported and indigenously developed equipment. The Chinese coal industry made a near- quantum jump with massive implementation of Longwall technology, especially the new generation of Longwall equipment10 . Through sustained R&D efforts over the fast three decades, China has made a major break through in Longwall technology for thick seams using sub level caving (Soutirage) has emerged as the world leader in this area with record production levels and manufacture of equipment packages for sub-level caving6, 11, 12 . Coal production in China soared to two Bt per annum from one billion, and in excess of 95% of coal is being produced by underground mining technology, in which Longwall technology is contributing major share. By careful selection of the geological conditions and equipment, several Longwalls are now producing at around 9 Mt per annum and have achieved one Mt per month1 . The coal measure formations of India and Australia are similar as both belong to the lower Gondwana. Australian coal mining industry have achieved a great success in mechanized coal production, while in India, the strata control and rock mechanics problems created havoc for the mechanization in the beginning itself. A review of support capacity of two countries shows that support capacity of Australian Longwall faces is almost double that of our Indian Longwall mining faces13 . Annual average of around 3 Mt with a commensurate OMS has been reported from Australia with 24 Longwall faces giving an annual production of 72 Mt14 . The national average production from a Longwall face in the USA was less than a million tonne in mid 80s; recent statistics indicate that the country produced around 270 Mt of coal from 52 Longwall faces, which means an annual average of more than 5 Mt from a face with an average OMS exceeding 10014 . EXPERIENCE OF LONGWALL MINING AT SCCL Longwall mining was introduced in SCCL for the first time in GDK-7 Incline in the year 1983 and after successful completion of two faces equipment was shifted to GDK-9 Incline in 1986, where the Longwall face collapsed due to inadequacy of the support capacity. Two more Longwall packages were introduced in VK-7 and JK-5 Inclines in 1985 and 1990 respectively. There after three more Longwall packages were introduced in GDK-11A during 1992-93. Capacity of powered roof supports in the above mines is of 4x360 tonnes (t) and 4x450t. Later higher rated supports one set in each GDK-10A, GDK-9 Inclines and two sets in PVK 5 Incline were introduced. The support capacity in the above mines is of 4x800t and 4x760t with a support density of 110 to 120 t/m2 respectively. So far, 10 Longwall packages have been introduced in seven mines with collaboration of foreign countries like UK, and China, details of which are as given in Table 2. Presently two Longwall units are working in GDK-10A and GDK-9 Inclines, while the units in other mines were surveyed off /not in working condition. The faces at SCCL in GDK-7 and VK-7 Inclines did well in comparison with other faces, which experienced caving difficulties. In early nineties with the introduction of higher rated supports the performance of Longwalls improved to some extent. Barring the catastrophic failure of Longwall faces of Churcha, Kottadih and Dhemomain of Coal India Ltd., faces at GDK-10A, PVK, JK-5 and VK- 7 gave consistently good results. The production performance of Longwall faces from SCCL and CIL is as shown in Fig.1. Fig.1: Longwall production in CIL and SCCL
  4. 4. 162 A Retrospective Assesssment of Longwall Mining With A Focus on Successful Mechanised Underground Mining Technology So far, nearly 68 Longwall panels of varying face lengths 60m to 150m have been worked at a depth range of 45 to 400m. The production performance of five Longwall units viz; JK-5(1 unit), VK-7(1 unit), GDK-10A (1 unit) and PVK (2 units) is as shown in Fig.2. History of Longwall mining in SCCL reveals that performance of almost all the Longwall units was better for first two to three years when compared to later. The average production at GDK-10A and PVK is about 4 Lakh tonnes (Lt) and 3 Lt per annum respectively, while other Longwall units were below 3 Lt per annum. In JK-5 Incline production above 3 Lt per annum obtained after successful working under caved Longwall goaves. This reflects that numerous high productive Longwall faces that have been installed did not perform to the level as envisaged. It can also be observed that high capacity support faces performed better than other faces in respect of production and strata control point of view. These Longwall units, apart from working creditably, have provided an opportunity for SCCL engineers to study the equipment and support parameters vis-à-vis the geo-mining conditions prevailing in the SCCL mines. Presently Sccl is planning high capacity longwalls at Adriyala shaft blocks, Jallaram shaft blocks of Ramagundem region and Kakatiya longwall projects of Bhupalapalli area. The Kakatiya longwall project is undergoing a process of TPO( Technology Provider cum Operator)for longwall mining. Table 2 : List of Powered roof supports (PRS) deployed at Longwall faces, SCCL, India. Mine Initial / Date of Capacity Rated Shifted Commission Make of PRS TPD GDK.7 Incline Initial 02-09-1983 Gullick Dobson, UK 4 x 325t to 4 x 360t GDK-11A Incline Unit-I Initial 01-04-1991 Gullick Dobson, UK 4 x 430t Unit-II Initial 10-10-1991 MECO, UK 4 x 450t Unit-III Initial 16-12-1992 Gullick Dobson, UK 4 x 450t VK-7 Incline Unit-I Initial 13-06-1985 Gullick Dobson, UK 4 x 360t Unit-II From GDK-11A 13-07-1994 MECO, UK 4 x 450t 1600 PVK Unit-I Initial 21-08-1995 CME, China 4 x 760t 2200 Unit-II Initial 22-06-1996 CME, China 4 x 760t 2200 JK-5 Incline Initial 06-06-1990 Gullick Dobson, UK 4 x 450t 2000 GDK-9 Incline Unit-I From GDK-7 31-01-1986 Gullick Dobson, UK 4 x 360t Unit-II Initial 05-02-1996 MECO, UK 4 x 750t to4 x 800t 1900 Unit-III From PVK Unit -I 21-08-1995 CME, China 4 x 760t 2200 GDK-10A Incline Initial 18-10-1994 MECO, UK 4 x 800t 2200 TPD : Tonnes per day Fig. 2 : Production performance of different Longwall units, SCCL
  5. 5. V. N. S. Prasad, M. U. Siva Sankar, Prof. S. K. Mukhopadhyay and Prof. Debasis Deb 163 The availability and utilization of the Longwall equipment at different mines of SCCL is depicted in Fig.3. It was obvious that, the average availability of all the units is 65 to 75% of scheduled shift hours (SSH), where as their utilization is only 17.5% to 22.5% of SSH. The average utilization of the equipment of all the above units is only 28 to 38% of machine available hours. The utilization and availability of Longwall equipment is far below the world Longwall equipment standards. From the analysis, the down time percentage was on the higher side in which major causes were breakdowns in outbye transport, shearer, AFC, Powered supports, stage loader/gate belt conveyor, electrical, frequent movement and shifting of equipmentatfaceandotherreasons.Thebreakdownanalysis of powered support Longwall (PSLW) face, CME make, at PVK from 1996 to 2000 is given in below Table 3. Table 3 : Breakdown analysis of PSLW face at PVK, SCCL. Year Shearer AFC PRS Power BSL Crusher Gate Electrical others Total BD Worked Hours lost pack belt hours hours due to other reasons 96-97 370.25 121.25 5.10 2.00 29.10 1.30 11.55 34.60 10.45 586.20 1742.20 972.00 97-98 358.25 161.00 31.10 15.20 207.25 0.25 27.00 20.00 39.00 861.30 2147.35 531.00 98-99 127.30 224.00 15.40 2.50 62.25 - 47.15 2.35 127.45 612.35 1260.50 777.00 99-2K 569.15 240.00 88.20 10.45 160.00 3.40 120.45 27.00 523.00 756.55 2042.25 1402.00 Fig. 3 : Comparison of Percentage of Availability and Utilization of different Longwall units, SCCL
  6. 6. 164 A Retrospective Assesssment of Longwall Mining With A Focus on Successful Mechanised Underground Mining Technology FACTORS RESPONSIBLE FOR LOW UTILIZATION AND HIGH DOWNTIME OF LONGWALLS Minor geological disturbances like faults, erratic appearance of sandstone modules affected the Longwall operations to a large extent. Prominent cavities, roof breakage or roof collapse due to dynamic loading over supports caused bad roof/face conditions under coal or sandstone as immediate roof. Bad face/roof conditions also cause breakdown in face machineries, like damages in shearers while negotiating various geological disturbances, overloading of shearer drive, damage of legs of powered supporters, chain snapping of AFC, etc. Frequent shifting of equipment from one panel to another panel, i.e., salvaging and installation of face equipment also led to low utilization and high downtime. However, general views of the problems faced by various types of face machineries in SCCL are described as under. Shearer Some of the common and major breakdowns in the shearers observed are haulage breakage, main and auxiliary hydraulic system malfunctioning, bearing of the first and second motion shafts in the gear head gear boxes getting damaged, failure of the oil seals in the trunion shaft of the ranging arms and in the motor, failure of gear pumps for lubricating oil for ranging arms, gears and bearings, scouring in the ranging arm cylinder liner, failure of pick holders, failure of the hinge pins connecting the ranging arms with under frame sprocket tooth. The downtime due to breakdowns increased from 3% to 6% with indigenous spares in comparison with original equipment (OEM)15 . AFC (Armored Face Conveyor) & BSL (Beam Stage Loader) Indigenization of all parts of AFC resulted in frequent break downs. OEM supplied gave life of 3.0 Mt. Where as Indigenous AFC gave a life of 0.7 to 0.8 Mt only. In comparison with OEM the breakdowns increased from 3.5 % to 8 %15 . The major problems faced are failure of rigid section fastening at two drive ends, failure of blind shaft bearings and oil seal journals at oil seals, jamming of chain in the bottom race of the line pan, snapping of chain in the top and bottom of the AFC, failure of AFC flight bars, failure of chain connectors, breakage of AFC pans, failure of fluid couplings of the drives and excessive chain elongation As BSL is almost similar to AFC, only problems unique to stage loader are frequent breakdown of the tail end idle sprocket and its bearings, elongation of the TOB chain, sometimes due to creep of AFC and weak fastening of the lump breaker over stage loader, fast wearing of the convex and concave pans of the bridge section. Powered Supports and Power pack Some of the common and major breakdowns in the powered supports and power pack are frequent troubles with the control valves, frequent failure of hydraulic hoses and connectors, leakage of leg seals, premature operation of the bleed valves, damage of reverse thrust rams, failure of relay bar piston fixing brackets due to less collar thickness, pumping of hydraulic fluid at a pressure below the required level, frequent failure of the unloader valve, improper functioning of the accumulators, excessive leakage in the system owing to the use of locally made components as no original spares are normally available causing excessive pressure drop. Improper maintenance of emulsion resulted in rusting and failure of hydraulic valves and increased bypasses in the system. However, high breakdown times of face machineries can be summarized as non-availability of imported spares, lack of proper quality of indigenous spares, absence of planned maintenance and reporting, apart from unexpected geological features and disturbances. Reasons for Slow Progress of Longwalls Main reasons for under rated performance of Indian Longwalls particularly at SCCL include technical as well as financial constraints. They are; • Long walls were introduced mostly in the blocks left over by working Bord and pillar method. Clean and extensive blocks have not been identified. Even the
  7. 7. V. N. S. Prasad, M. U. Siva Sankar, Prof. S. K. Mukhopadhyay and Prof. Debasis Deb 165 smaller blocks, which were identified, were of inferior grade coal. • Long wall had to co-exist with the conventional mining in most of the mines, which caused management problems. • There were some deficiencies in the imported spares management and the supplies were not reaching in time. • Development could not keep pace with the extraction of Long wall panels; slow progress in the formation of Long wall panels affected the performance. • Large expansion in opencast mining in the past two decades provided cheaper and safe method for bulk coal production and as a result long wall had to take back seat. • Coal companies were sensitive to the failures of a few long wall faces and were not prepared to risk huge investments. • Infrastructure was not suitable to support the higher production. • Geological and geotechnical conditions were more difficult than expected. • Problems in the maintenance of the equipment. By and large contributory factors that have been identified for the not so successful operation of Longwall systems in India converge on the following; • Inadequacy of geological and geotechnical assessment of the Longwall locales. • Flawed equipment selection with inadequate rating of supports, shearer and coal clearance systems. • Management failure in planning, operation, provision of service back-up and spares availability. • Absence of a viable manufacturing capacity for Longwall equipment. • Equipment sourced from many suppliers with no accountability. • Bureaucracy of end user regarding availability of spares supply. • Lack of suitably trained management. SAGA OF SUCCESSFUL LONGWALL MINING OF CHINA In the recent decade, remarkable progress has been made in realization of high output and high efficiency in coal industry, especially in state-owned key coal mines in China. The reasons are: China from the very beginning as a policy adopted wholesome approach for large scale Longwall mechanization in their UG mines. Their approach was very methodical and it took into account their own social and economic conditions. Instead of instantaneously jumping into hi-tech mechanization only in some isolated mines, they introduced Longwall technology stage by stage with incremental technology development. The economy in China has been developed rapidly under the new economic system; the continuously increased demand for coal promoted coal mines to increase production. Coal mines have become independent enterprises, assuming sole responsibility for profits and losses. State is no way responsible for financing. On the other hand, the state-owned coal mines have a relatively unwieldy organization, with higher value of fixed assets, over staff members and workers. The Chinese government has worked out policies for reforming the existing underground mines and construction of new mines, preferential terms can be given to any project which can meet with the principle of high output and high efficiency. This has promoted the development of high output and high efficiency in coal mines. The number of working Longwall faces in state- owned key coal mines is reduced from 2313 in 1984 to 1499in1994,andthetotaloutputofarelevantfaceisincreased from 320 Mt per annum to 370 Mt per annum, which depicts a great progress in Longwall mining in China 16 . The development of science and technology in recent years has delivered equipment and technology with
  8. 8. 166 A Retrospective Assesssment of Longwall Mining With A Focus on Successful Mechanised Underground Mining Technology more varieties and better performances, which has made it possible for coal mines to realize a high-output and high- efficiency. Based on the reasons mentioned above, various measures have been taken in coal mines, especially in state-owned key mines in China, to realize a high output and high efficiency. Manufacturers concerned for coal mines and department of scientific research have been very active to take part in this work, delivered a lot of new technology and new equipment to promote the development of high output and high efficiency in coal mines, and a remarkable success has already been achieved. For achieving high production and productivity lot of work have been done in the field such as such as: increasing the length of a working face, selecting equipment used on a working face with a large power and high performance, improving the mechanization of auxiliary procedures, (e.g. Auxiliary haulage system and supports on ends of a face, etc), popularizing the communication control system used underground and strengthening control system used underground, improving the reliability of equipment and strengthening the technical training to staff members and workers of the mine9 . Based on the statistics, during 15 years, i.e., till the middle of 1995, a total of 820 kinds of equipment of ten categories with different performances, models and specifications used in coal mines had been developed with a tendency to satisfy the demands of coal mines of a high output and high efficiency. The capacity of the equipment, such as shearer, scraper conveyor, and emulsion pump has been increased substantially to negotiate unforeseen circumstances too. AREAS TO BE ADDRESSED Based on the past experience of Longwall mining in India in comparison with China, the following thrust areas are also to be addressed for successful implementation of Longwall mining in India to meet the global standards: • Indigenous development of qualitative Longwall equipment is to be encouraged for introduction of Longwall faces at several mines. • The manufacturing companies of India such as MAMC and Jessop which have been planned for infrastructure development of Longwalls have to be reconstructed. Private sector participation in infrastructure development must be encouraged. • More number of Longwall blocks to be identified to encourage manufacturing of equipment in India. • Approval process from Government of India, for implementation of new projects should be fast to bring projects on stream at the earliest. • Rigid quality control and performance testing should be done for the spares manufactured indigenously. • Use of high capacity supports of up to 1280 tonnes providing a load density of 135 to 140 t/m2 are to be used under Indian geo-mining conditions. • Even with the use of high capacity supports may not give satisfactory roof condition during impending roof weighting. In such cases artificial means of induction of caving by hydraulic fracturing or other means is to be considered. • Orientation of Longwalls correctly with respect to horizontal stress is critical for strata control during development and Longwall extraction. • Effective monitoring of strata and support behavior and meticulous maintenance of equipment are the keys for the success of Longwalls. • Interactive evaluations of mine plans with integrated geological data have to be established for Longwall workings. Automation should be implemented for planning and monitoring Longwall workings. • Collieries should develop a highly competent maintenance group with suitably defined responsibilities and a good team leadership. The members should be properly trained by experts both at site as well as in the manufacturer’s works. CONCLUSIONS Mechanised Longwall mining has emerged as the most successful production technology in the global coal mining scenario. The effective application of enabling
  9. 9. V. N. S. Prasad, M. U. Siva Sankar, Prof. S. K. Mukhopadhyay and Prof. Debasis Deb 167 technologies of hydraulics and electronics coupled with the use of heavy duty supports and equipment during last three decades have helped Longwall technology to scale new heights of production and productivity. Introduction of fully mechanized Longwall technology was made in China and India almost simultaneously. No comparison between these two developing nations can be made in terms of the success parameters. The basic factor is the difference in attitude and determination to go ahead with this globally accepted technology. Many factors contribute to preventing most Longwall installations from producing anything but a fraction of their theoretical capacity. Longwall should be promoted as a technology mission, thrust areas are to be given due consideration to succeed Longwall technology as in other developing country like China. A high level expert group is to be constituted at national level to promote, coordinate and discuss different aspects related to Longwall technology. Training with regard to the problems anticipated in the countries in which such problems are already overcome so as to prepare guidelines for future Longwalls. Concrete efforts are required by the mining inspectors, policy makers, coal companies, research organizations and equipment manufacturers to translate the ideas into concrete action and reap the benefits of Longwall technology in the years to come. ACKNOWLEDGEMENTS The views expressed in the paper are those of the authors only and should not be attributed to organization they belong. REFERENCES 1. David Johnson. “The Need to Fully Mechanise the Underground Coal Industry in India” 1st Asian Mining Congress 16-18 Jan, 2006 pp 209-215. 2. Kumar, Shashi. “CIL roadmap for meeting energy challenges”, Coal Summit, 2005, pp 1-21. 3. W V Linden, “Worlds best Longwall Mining Practices: what is applicable to India, in Mining Challenges of 21st century”, (editors: A K Ghose and BB Dhar), APH Publishing corporation, New Delhi, 2000, pp 23-27. 4. A K Ghose. “Mechanised Longwall Mining in India – collating the decadal experience (1978-1987). Journal of mines, Metals & Fuels, June, 1988 pp 267-273. 5. A K Ray et al., “Cavability assessment of roof rocks to understand interaction of strata and support at Longwall face”, Minetech, Vol.26, No.4, Jul-Aug, 2005, pp 16-28 6. A K Ghose. “Why Longwall in India has not succeeded as in other developing country like China”, IE (I) Journal, Vol. 84, Aug 2003, pp 1-4. 7. A K Ghose, et al., “Cavability of Indian coal measures rocks for Longwall design – An Appraisal”, IE (I) Journal, Vol. 67, November 1986. 8. S.K.Sarkar. “Mechanised Longwall Mining – the Indian Experiences”, Oxford 7 IBH Publishing Co. Pvt. Ltd. 1998. 9. Mukhopadhyay S K., Kumar D. “Longwall Mining in India – Mapping the Short comings through Experience and Sighting the Benchmark for Successfully Application under Chinese Guidelines”, IE (I) Journal-MN Vol.84, February, 2004, pp.43-54. 10. A.K.Ghose. “Design of Longwall Faces in India – Agenda for decisions”, Longwall Face Supports Development – Special Number, Journal of Mines, Metals & Fuels, March, 1985, pp.67-74. 11. Peng Sheng. “Recent Developments – and some problems – in the application of fully mechanized Longwall Mining, using sub-level caving, in China”, Coal International, November 1998, pp.224-231. 12. Samir Kumar Das. “Highly Productive Thick Seam Mining System - A Break Through”, proceedings of 3rd National Seminar on Rock Excavation Techniques, 8-9 January 2005, pp.66-70. 13. RajendraSinghetal.,“Geo-technicalConsiderationsfor Underground extraction of thick Coal seams in India’, Proceedings of Nat. Seminar on Geomechanics and Ground Control – 2003, pp 205 – 216. 14. S.K.Sarkar and A.K.Ghose. “Longwall Mining in India – Quo vadis?” 1st Asian Mining Congress 16-18 Jan, 2006 pp 216-224 15. Back ground material for “Brain storming session on Longwall mining, SCCL” conducted on 04.01.2007, Kothagudem. 16. L Zhihong, ‘High Output and High Efficiency in Coal Mines of China.’ Seminar on High Production Technology for Underground Mines, The Mining, Geological and Metallurgical Institute of India, July 12-13, 1996, P 315.