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Procedía Earth and Planetary Science 11 (2015) 189 - 194
Global Challenges, Policy Framework & Sustainable Development for Mining of Mineral and Fossil Energy Resources (GCPF2015)
Reliability Study of42 cu.m Shovel and 240 Te Dumper Equipment System with Special Reference to Gevra OCP,
SECL, Bilaspur
Sanjay P. Dubeya, Dr. Manish D. Uttarwarb, M. S. Tiwaric
a Gevra Project, SECL - 495452, India. bDepartment of Mining Engineering, RCERT, Chandrapur- 442403, India. cRamdeobaba College of Engineering and Management, Nagpur -440010, India.
Abstract
The coal still remains and will continue to stay at the centre stage of India's energy basket due to occurrences in abundance thus fetching global rank both in respect as a producer and as a possessor, despite the intensified movement across the world over reduction of carbon dioxide emissions. Opencast mining sharing this onus responsibility, it is in this standpoint the development and deployment of innovative technologies are an essence for the coal mining industry to be cost effective, ensure maximum recovery coupled with higher safety. Over the years since nationalization, we have witnessed mechanization of underground mining facing stiff limitations due to number of restrictive geo-mining parameters and thus harnessing the coal output. Thus on a long term perspective, a need is felt to frame our strategy focusing on opencast production with concerted efforts on innovative technologies specifically to winning of moderate to greater depth coal reserves. It was against this backdrop, Gevra OCP deployed 42 cu.m shovels and 240 Te dumpers with O.I.T.D.S (Operator Independent Truck Dispatch System) as a most modern and innovative system. Today for the indigenous coal sector, the system stands as a hallmark of production giving minimum exposure to risk and providing logical and systematic method of production. The capacity and productivity of these equipment systems depends primarily on work conditions, geo-mining profile and deployment methodology. This paper attempts at reliability study of these machineries. The estimates of reliability are carried out using statistical analysis of failure data sets coupled with review of system deployment conditions which accounts for geo-mining and operational parameters of the mine.
© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).
Peer-reviewunderresponsibilityoforganizingcommitteeoftheGlobal Challenges,PolicyFramework& SustainableDevelopmentforMiningofMineralandFossilEnergyResources.
Keywords: Opencast coal mines, shovel-dumper equipment system, productivity, reliability.
1. Introduction
Every year various types of equipment for use by the mining industry are manufactured throughout the world, and that this expenditure is increasing rapidly. Today, the global economy is forcing mining
1878-5220 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of organizing committee of the Global Challenges, Policy Framework & Sustainable Development for Mining of Mineral and Fossil Energy Resources. doi:10.1016/j.proeps.2015.06.023
companies to modernise their operations through increased mechanisations and automation and that the Indian mining sector is not an exception to this.
India is the world's third largest country having geological coal resources of 301 Billion Tonnes as on 1.04.2014. In India, coal accounts for almost two-third of electricity generation. The share of the opencast mining increased from 26% to 88% from the year 1974 to 2014. The changing global economic scenario requires innovative and improvised mining systems. The demand scenario of coal is highly dynamic and is expected to grow beyond what is planned for the near feature. In this context, the opencast coal mining sector is witnessing a continuous rise in the equipment capacities employed for the removal of overburden and coal. Generally it is influenced by the following important factors.
• High production requirements to meet ever rising demands.
• Need to handle increased depth of overburden and
• Increased stripping ratio for the given mines.
2. Gevra OCP at a glance
Gevra Opencast Project opened in the year 1981 has sanctioned capacity of 40 MTPA with an average stripping ratio of 1.3 cum per tonne. The mine features four major coal seams having combined thickness ranging from 117 m to 174 m and gradient ranging from 1 in 6 to 1 in 12. The depth of mine stands at 160 m and that the maximum depth planned is 300 m.
Due to increase in thickness of coal seam and smooth seam gradiant, surface miner is used for coal production. The thickness of coal varies from 10 m to 55 m depending on the seam. The coal benches are wide upto 20 m with height varying from 10 m to 20 m and have slope angles of 60° to 75°. Approximately 90 % of coal extraction is being done by deploying 8 Nos. of Surface Miner for cutting in-situ coal slice by slice on the floor of the bench and remaining 10% coal extraction is being done by conventional back-hoe and dumper combination. Loading & transporting from surface miner face is being done by Pay-loader and tipper combination. The ratio of coal production for the conventional shovel dumper system and surface miner- pay loader - tipper system is near about 1:11.
OB removal is being done by deploying shovel-dumper combination coupled with large diameter deep-hole blasting employing site mixed slurries. The bench width varies from 30 to 35 meters whereas bench height for 42 cum. shovel is maintained at 20 m and 10 m for other shovels. Some of the overburden removal task is outsourced and is approximately 25% of the total overburden handled in the project. The daily consumption ofexplosives is approximately 60 tonnes.
Gevra opencast project is one of the prominent mines of S.E.C.L having annual coal and overburden production targets for the year 2014-2015 slated at 40 million tonnes and 49 million cubic meters respectively. Table 1.0 given below depicts overburden and coal production statistics and stripping ratios handled for the eight year period.
As can be observed from the table above, the coal production has achieved a growth of 33% in the last 8 years that is handled by eight Continuous Surface Miners' of vivid configurations employed on hired basis in the project. During the period, the stripping ratio has almost doubled signifying gigantic task of OB removal. This stupendous target was achieved by deploying an array of high capacity Heavy Earth Moving machineries i.e. primarily shovel-dumper equipment system for handling OB at the Gevra OC Project from time to time and is shown in Table 2.0 depicted below.
Table 1. Production statistics of gevra OCP, SECL, Bilaspur
Year Over burden (million cum) Coal (million Te) Stripping ratio (cum/Te)
2006-2007 12.38 27.22 0.455
2007-2008 11.46 29.0 0.395
2008-2009 19.6 31 0.458
2009-2010 25.6 35 0.638
2010-2011 30.7 35 0.874
2011-2012 22 35 0.629
2012-2013 23.3 35 0.665
2013-2014 35.3 38.7 0.911
(Source: Gevra OC Project data base)
Table 2. Details of HEMM deployed at Gevra OC Project
Dumper Shovel Dozer/Grader Drill Others
BH35 P&H 1900 Caterpillar D-ll T Atlas Copeo Pit Wiper Water Sprinkler
BH120 O&K 10 Cum Komatsu D-475-A5-E0 Atlas Copeo Igm 30 Tyre Handler
BH100 O&K 15 Cum Komatsu D-475-A5 Recp 750(D) Cranes
Terex 100 Te Bucyrus 10 Cum Beml Bd-355 Recp 750 (E) Fork Lifter
Terex 120Te Bucyrus 42 Cum Caterpillar D-8r Ingersol Rand Truck Mounted Cranes
Komatsu 100 Te P&H 4100c Caterpillar 24m Recp 30-D Diesel Filler
Cat 240 Te Tata Hitachi Pc Caterpillar Gd-825 Recp 30-E Man Lifter And Others
(Source: Gevra OC Project data base)
All the above listed machineries are operational at the project and most of them have yielded expected performance. However the deployed machineries faced various inherent operational constraints mainly due to ever increasing stripping targets coupled with below mentioned factors which have found to have bungled them whilst achieving the prevailing production targets.
• Non availability of spares.
• High cost OEM.
• High machine marching time.
• Scanty data base of geo-mining conditions.
• Poor planning of excavation.
• Poor blasting performance.
• Unskilled labour force.
• Poor haul road condition.
• Poor maintenance systems.
It was therefore against this backdrop, the Gevra OCP operators and management has introduced Bucyrus 495 HD Shovel - 240 Te Dumper combination with MARC (Maintenance and Repairing Contract) in February 2010 and October 2010 respectively for a period of 12 years. Similarly keeping in view, another P&H 4100c shovel with MARC has been introduced in the month of June'2014. Since then the productivity of the mine is observed to have increased inspite of revision in wages and salaries and increasing costs due to POL, electric power etc.
Thus, it can be seen that Gevra Ocp possesses an array of mining equipments which are more complex and sophisticated warranting for increased capital costs. This in turn makes it cost ineffective for the mine to have standby units. To meet the prevailing targets, the project thus demands not only for better but increased equipment reliability. Reliability is a good performance indicator of overall equipment condition and is defined as the probability that a piece of equipment will perform its function satisfactorily for the desired period of time when used according to specified conditions.
2. Performance ofexcavators & shovels
The year wise production performance of the duo of 42 cum shovels deployed for handling OB at the project during the period from 2010 to 2014 is shown in the Table 3.0 given below.
Table 3. Production Statistics of 42 Cum Shovels during the period 2010 to 2014
Shovel name Make/ specification 2010-11 Production (figures 2011-12 2012-13 in cum) 2013-14
Partha Bucyrus - 42 cum 5655963 4927118 6246972 6973304
Krishna Bucyrus - 42 cum 2749983 4758360 6038048 7049966
(Source: Gevra OC Project data base)
Table 3.0 given above shows the production statistics for the duo of 42 cum capacity shovels that have shouldered the onus of handling 52.20% ofTotal OB justifying their deployment at the project.
Table 4. Comparative Analysis of Excavator/Shovel for OB Production
(All figures in cu.m.)
Year All shovels excluding 42 cum (including outsourced ob ) For 42 cum shovels
Overall production No. of machines Average Overall production No. of machines Average
2008-2009 26542700 13 2041746 Nil — —
2009-2010 29162745 12 2430228 Nil - —
2010-2011 41911885 15 2794125 8405946 2 4202973
2011-2012 46373836 13 3567218 9685478 2 4842739
2012-2013 43180185 15 2878679 12285020 2 6142510
2013-2014 49757138 16 3109821 14023270 2 7011635
From the Table 4.0 given above, it can be observed that the Shovel-Dumper equipment system of the project under consideration has yielded approx. 69% oftotal target OB production and the rest is made up by outsourced agencies. However it can also be seen that there is a noticeable difference in production figures for the year 2010-2011 and 2011-2012 which is attributed to reasons as mentioned below.
• Commissioning of the shovels in the midst of the given year.
• Initial phase needing time in respect of operational accommodation.
• Shortage of dumper tyres thus restricting their availability.
• Lack of supportive infrastructure and facilities and
• Lack of Skill up-gradation for the operators.
3. Reliability of 42 cum shovels and 240 te dumpers
Reliability of the equipments plays an important role in cost effectiveness of the system. Reliability in most simple form is defined as the probability of an item to perform a required function under stated conditions for a specified period of time. This way it helps in assuring the system performance in quantitative terms. The reliability models ofa system are essentially a model based upon the concept of probability and statistics.
Considering the available reliability techniques like fault-tree methodology, correspondence analysis to classify shovels in terms of repair durations, Reliability Predictions based on Mean Time Between Failures etc and the varying degree of reliability required for different situations, the reliability assessment of 42 cum shovels and 240 te dumpers system is thought over to be an essential for the better performance of this innovative and most productive technology.
3.1. Breakdown analysis
The detailed study oftotal hours of deployment under various heads for 42 cu.m shovels and 240 Te dumpers during the period from 2011-12 to 2013-14 is carried out. Considering the nature of breakdowns, they are classified as mechanical, electrical and operational types.
It was observed from the compiled and analysed data that the major breakdowns in 42 cum shovels are attributed to Electrical fault, Track part, Dipper, Hoist-Crowd-Swing system, Latch and Propel system, Air compressor, Trip rope, Bucket, Lubrication, Brakes, Machine struck up, Trailing cable damage, Improper operation and Accidental damage.
Whereas in case of 240 Te dumpers they are attributed to Air leakage, Hydraulic system, Transmission system, A.C. problem, Dump body, Torque converter, Battery, Dump cylinder failure, Suspension problem, Tire problem, Engine, Brakes, Fuel supply, Machine struck up, Improper operation, Stairs, Guards and Body hoist.
The Tables 5.1 and 5.2 given below shows the breakdown hours, maintenance hours, idle hours and working hours as percentage of the scheduled shift hours for the 42 cu.m shovels and 240 Te dumpers respectively.
Table 5. Percentage classification of total hours (for shovels)
Year B'down Hrs Maint. Hrs Idle Hrs Work Hrs Availability % Utilisation %
2011-12 60.0 3.58 3.71 36.71 93.04 56.25
2012-13 64.44 4.46 4.76 26.34 91.50 64.33
2013-14 56.51 7.74 3.00 32.75 92.16 56.50
Average 58.98 5.26 3.82 31.93 92.23 59.02
. Percentage classification of total hours (for dumpers)
Year B'down Hrs Maint. Hrs Idle Hrs Work Hrs Availability % Utilisation %
2011-12 33.45 55.70 1.49 9.36 97.83 37.83
2012-13 49.88 22.85 2.27 25.00 94.98 49.66
2013-14 31.90 53.30 1.46 13.34 95.91 31.41
Average 38.40 43.94 1.73 15.90 96.24 39.63
The tables given above showing the breakdown hours, maintenance hours, idle hours and working hours in percent for the 42 cum shovels indicates that the breakdown hours are significant but then the maintenance and idle hours are as much less as compared to the breakdown hours thus rendering a fairer utilisation of the given equipments. Whereas breakdown hours, maintenance hours, idle hours and working hours in percent for the 240 Te dumpers indicates that although breakdown hours are a less compared with the maintenance hours but then when both accounted together is a much significant thus rendering poor utilisation ofthe given equipments.
3.2. Reliability analysis
Reliability is the major constraint which many of the mining industry opt for. It is helpful in monitoring performance, maintenance interval etc. of the given equipment. Correct decisions can be made by way of increasing length ofthe intervals which decreases maintenance costs. Economy and manpower management plays a prominent role in reliability analysis.
The succeeding section highlighted details of breakdown under various heads in respect of 42 cu.m shovels and 240 Te dumpers followed by analysis of total available hours. The reliability analysis is being done based on probability. Here the probability of failure P(F) is being calculated, the overall probability of failure for 42 cu.m shovels and 240 Te dumpers under consideration comes out to 0.052 and 0.433 respectively. The overall Reliability of42 cu.m shovels and 240 Te dumpers after probability estimates comes out to be 94.73 and 56.63 percent respectively.
Table 7. Reliability analysis for 42 cu.m shovels and 240 te dumpers
Year P(Failure) % P(F) Reliability
For 42 cum Shovels
2011-12 0.03616 3.62 0.9638
2012-13 0.04464 4.46 0.9554
2013-14 0.07732 7.73 0.9227
Average 0.05271 5.27 0.9473
For 240 Te Dumpers
2011-12 0.5512 55.12 0.4488
2012-13 0.2284 22.84 0.7716
2013-14 0.5215 52.15 0.4785
Average 0.4337 43.37 0.5663
3.3. Interpretations of the analysis
From the above conducted study, it can be stated that
• The breakdown of the shovels is observed to have increasing trend.
• The overall reliability of the shovel depicts decreasing trend year by year.
• This calls for review of deployment methodology of the shovels accounting for geo-mining profile and work conditions since there are many factors that, directly or indirectly impact mining system reliability. For example, geology results in variation in digging conditions for the shovel, mine plan calls for regular shifting of equipment as different areas are to be mined, a blast can frequently stop the equipment operation etc.
• Shovel requires more attentive focus on maintenance interval.
• The probability of failures in case of dumper is much significant and thus resulting in relatively more maintenance requirements.
• For dumpers, needs more attention on similar type recurring type of breakdowns so that maintenance time and cost can be reduced.
4. Conclusions
It can be concluded from the above study and analysis that
• The reliability study is an essential for any machine for its better performance.
• Reliability analysis is not only helpful in objective assessment of the machine but also useful tool in such decision making for further deployment of the given equipments.
• The analysis indicates room for improvement in different aspects of the given shovels. Improving the maintainability of supporting dumpers is the important way to the reliability of the given equipment system.
• Aspects of failure behaviour of machines need to be analysed briefly for improvement in ongoing machine performance.
• For the indigenous coal sector, the system under discussion stands as a hallmark of production giving minimum exposure to risk and providing logical and systematic method of production.
Acknowledgements
The work presented in this paper forms a part of the Post Graduate Study in Mining Engineering of the first author. The author expresses his thankfulness towards the supervisors of the study and Department of Mining Engineering, RCERT, Chandrapur for providing varied facilities due to which this research paper could take the present shape. The permission and subsequent field support from Gevra opencast coal mine of SECL selected for the study is deeply acknowledged with thanks. The views expressed in this paper are those of authors and not necessarily of the organizations they represent nor of the sector under study.
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