A PRESENTATION ON RETROSPECTIVE ASSESSMENT OF INDIAN LONGWALL MINING : A PRESENTATION ON RETROSPECTIVE ASSESSMENT OF INDIAN LONGWALL MINING V.N.S.Prasad.M, UM(SCCL)
U.Siva Sankar, UM(SCCL)
Prof. Mukhopadhyay S K., IIT, KGP
Prof. Debasis Deb., IIT, KGP Presented at 3rd Asian Mining Congress, Kolkata Introduction : Introduction In this era of nuclear energy agreements coal occupies the centre-stage in the energy economy of developing countries like 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 production.
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.
In order to keep pace with the growing Indian economy at the rate of 8 to 9%.
Mechanized Longwall mining is a sustainable option to achieve higher production and productivity Evolution of LW technology : Evolution of LW technology In the seventeenth century innovation of ‘Longwall’ system in Shropshire in England.
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 mining.
In India first mechanized powered roof support face, the new-age Longwall, was launched in August 1978 at Moonidih Colliery.
In India, 33 Longwall packages have been deployed to date in Coal India Ltd and Singareni Collieries Company Ltd in collaboration with U.K, Russia, China, France mostly funded by GOI.
During last 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 conditions. LW technology –Indian scenario : LW technology –Indian scenario Only a few of the faces could yield planned production level for initial three to four years of support life.
Majority of the Longwall faces in India have been worked under relatively shallow cover (< 200m) and significant problems on the caveability of the roof have been experienced.
Severe strata control problems at face resulting in damage of supports and increased downtime of equipments substantiated by improper matching of the sub systems.
An unsuitable locale selection incompatible with the selected supports due to improper pre-investigation. Slide 5: LW technology –China scenario In China, first fully mechanized face using chock type supports was introduced at Meiyukou colliery in 1963.
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.
Through sustained R&D efforts over the last 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 caving.
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 month LW technology –Australia and USA : LW technology –Australia and USA 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 faces.
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 Mt.
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 100. LW mining in SCCL : LW mining in 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. LW mining in SCCL : LW mining in SCCL So far, 10 Longwall packages have been introduced in seven mines with collaboration of foreign countries like UK, and China. 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.
So far, nearly 68 Longwall panels of varying face lengths 60m to 165m have been worked at a depth range of 45 to 400m .
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 5, JK-5 and VK-7 gave consistently good results. Slide 9: List of Powered roof supports (PRS) deployed at Longwall faces, SCCL, India Slide 10: List of Powered roof supports (PRS) deployed at Longwall faces, SCCL, India Production performance of different Longwall units of SCCL : Production performance of different Longwall units of SCCL Longwall production in CIL and SCCL : Longwall production in CIL and SCCL Downtime analysis of Longwalls (SCCL) : Downtime analysis of Longwalls (SCCL) 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.
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.
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. Downtime analysis of Longwalls (SCCL) : Downtime analysis of Longwalls (SCCL) Downtime analysis of Longwalls (SCCL) : Downtime analysis of Longwalls (SCCL) Downtime analysis of Longwalls (SCCL) : Downtime analysis of Longwalls (SCCL) Reasons for Slow Progress of Longwalls in India : Reasons for Slow Progress of Longwalls in India 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 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. Reasons for Slow Progress of Longwalls in India : Reasons for Slow Progress of Longwalls in India 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. Reasons for Slow Progress of Longwalls in India : Reasons for Slow Progress of Longwalls in India 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 manpower. SAGA OF SUCCESSFUL LONGWALL MINING OF CHINA : SAGA OF SUCCESSFUL LONGWALL MINING OF CHINA China from the very beginning as a policy adopted wholesome approach for large scale Longwall mechanization in their UG mines.
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. SAGA OF SUCCESSFUL LONGWALL MINING OF CHINA : SAGA OF SUCCESSFUL LONGWALL MINING OF CHINA 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 1499 in 1994, and the total output of a relevant face is increased from 320 Mt per annum to 370 Mt per annum, which depicts a great progress in Longwall mining in China SAGA OF SUCCESSFUL LONGWALL MINING OF CHINA : SAGA OF SUCCESSFUL LONGWALL MINING OF CHINA The development of science and technology (S&T) in recent years has delivered equipment and technology with more varieties and better performances and efficiency.
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)
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 mine THRUST AREAS TO BE ADDRESSED : THRUST AREAS TO BE ADDRESSED 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. THRUST AREAS TO BE ADDRESSED : 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. THRUST AREAS TO BE ADDRESSED Conclusions : Conclusions Mechanized Longwall mining has emerged as the most successful production technology in the global coal mining scenario.
The effective application of enabling 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. Difference is the determination to go ahead with this globally accepted technology. Conclusions : Conclusions “Change is the order of the day”.
Longwall should be promoted as a technology mission, thrust areas are to be given due consideration to succeed Longwall technology as in other developing countries 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 were 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. Slide 27: THANK YOU JAI HIND