Cost of truck haulage from mine pits are high and spiraling with inflation, diesel price, increasing haul distances and depths. Trucks, traditionally, have long been a favorite tool in surface mines for hauling material from the pits. The increasing strain of an inflationary economy has caused mine operators to look at alternatives to the longstanding workhorses (trucks) in material haulage.
The intent of any major modification of the time-honored material handling by trucks is to achieve the goal of a marked reduction in haulage costs; sufficient not only to recoup the capital investment, but to make the final product more competitive in today's world market. Due to increasing cost of truck haulage, now In-pit crushing and belt conveyor systems are one prominent alternative that has gained popularity.
The favorable economics of conveyor based haulage, especially in moving large volumes, has long been acknowledged. This has given impetus to significant developments over the last two decades in conveying systems and equipment. Such developments have resulted in improved equipment and system reliability, versatility and mobility. This may not be out of place to mention here the success story of fully mobile in-pit crushing & conveying system working in Piparwar project of CCL handling production @ 7.0 MTPA for around two decades & achieved highest OMS amongst CIL opencast projects.
Conventional belt conveyors offer a most economical method for transporting bulk materials at recommended inclination angles up to 12° to 18° for most common materials. Internal friction development and the induced dynamics of the moving conveyor belt limit the conveying angle. Higher angles approaching the internal friction angle could be achieved by reducing the dynamic effects. The inclination angle cannot, however, exceed the angle of internal friction of the material at the free surface.
Conveying angles beyond the angle of internal friction can be achieved by adding a cover belt which, when pressed against the material, will create a hugging action to prevent sliding at the contact surface.
The trend of reducing haulage costs with belt conveyors prompted the US Bureau of Mines to take it to the next level. The Bureau recognized the incline angle limitations for open troughed belt conveyors and the cost of accommodating the limitations. At the end of 1979 the US Bureau of Mines funded a major study entitled High Angle Conveyor Study. The Study ran from August of 1979 to December of 1981. In 1979 the Bureau of Mines, United States Department of the Interior, funded a major study entitled “High Angle Conveyor Study”.
(1) To advance the state-of-the-art in high angle conveying.
(2) To develop high angle conveying systems that would reduce the haulage costs in open pit mines.
The study was awarded to a prominent U.S. engineering company.
Joseph A. Dos Santos - Project Engineer was assigned to the Study.
The two volumes “High Angle Conveyor Study” report, published in 1981, included the Dos Santos theory and various sandwich belt conveying methods. Drawing from the success of the Loop Belt, Dos Santos Sandwich Belt systems included its best features and offered versatile profiles that could follow any high-angle path.
The Snake-Sandwich High-Angle Conveyor was cited as the preferred method and it was submitted for patent in 1981.
The Sandwich Belt High-Angle conveyor research and development was published more concisely in the 1982 landmark article “Evolution of Sandwich Belt High-Angle Conveyors” by Dos Santos and Frizzell.
Sandwich belt high-angle conveying systems use two smooth surfaced rubber belts that hug the conveyed bulk material, in a sandwich between them, along the carrying path. The hugging pressure develops the material's natural internal friction, successfully conveying it along any steep incline up to vertical.
A high angle conveying system is an economic and energy saving alternative, with the capability of achieving very high, steep angle lifts and capacities up to 10 000 TPH. High Angle Conveyor system deploys Standard locally available components and conventional belts.
Katharaopencast mine of Central Coalfields Limited lies in the South-Western part of the East Bokaro Coalfields in Bokaro District of Jharkhand. Mining in Kathara block was started in the year 1944 by M/s Anderson Wright and Company on behalf of M/s Kathara CoalCompany. It is very difficult mine with lot of faults & steep gradiant of coal seam.Ultimate depth of the mine shall be more than 150 m. The mine is producing washery GR IV coal @ 1.0 MTPA. Kargali seam is the bottom seam, where presently mining is in progress. The Kathara mine has been divided in three sections. The western section is being operated by MDO. The eastern section is not in operation at present & the pit floor is submerged in water. Presently ROM coal is being transported by 16 Te truck to Kathara Washery, where coal is being crushed to suitable size for washing. Excess ROM coal is transported by truck to railway siding.
Currently, there has been not sufficient exposure on this state of art High Angle Conveyor (HAC) technology in India. Indian Mine Planners & Consultants (IMPCON), Kolkata has been working on this technology for quite some time to apply this technology for the most economic solution of coal transport from deep mines.
IMPCON recently made a presentation at CCL (Hq), Ranchi on DSI Snake High Angle Conveyor technology. It had been agreed that a suitable mine in CCL shall be identified to explore the possibility of application of this technology to solve the transport problem in the mine.
Presently, at Kathara trucks are carrying coal from pit bottom from a depth of more than 100 m. It may be difficult to continue coal transport by trucks with further progress of mine, when the mine shall be deeper. Space at pit-bottom is limited and it will not be possible to install conventional conveyor for transport of coal from pit-bottom. The mine has 15 years of life & shall further go deeper by more than 50 m.
As such, CCL wanted S.K.Bag to visit KATHARA opencast mine to explore the possibility of application of High Angle Conveyor Technology for the best economic solution for coal transport . Accordingly, S.K.Bag had visited the mine on 8th Sept, 2016. After visit & studying the working mine plan, it is strongly feels that High Angle Conveyor shall be the only solution for this mine, since, DSI Snake High Angle Conveyor can be installed along the existing steep inclination of sidewall/highwall for carrying coal from pit-bottom to surface. Such steep gradient is beyond the limit of conveying angle of conventional conveyor. DSI Snake high angle conveyor shall be capable to transport coal along any slope (up to vertical) exceeding the dynamic stability angle of the transported material. S.K.Bag has made detailed study & economic evolution. The report is submitted as below.
Based on site visit, discussions & study of mine plan, S.K.Bag observed by combining the flexibility of truck transport in-pit with movable (skid mounted) crushing plant followed by DSI Snake High Angle conveyor along the side slope of existing in-pit overburden dumps coal can be transported at surface, wherefrom coal can be directly transported to washery by an overland conveyor. With such system it is very much possible to transport entire coal production for the main haul out of the pit completely avoiding a long path of trucks.
Truck haulage shall be restricted to travel between the working face and the in-pit crusher. The cost savings in transport by high angle conveyor over the present truck system shall be sufficient to achieve the pay back for investment in less than 5 years with target production 1.0 MTPA . It will be also possible to increase the production by 50% without any additional capital investment. This will achieve better IRR & PAY BACK.
Initially, two alternatives e.g, Alt 1 & 2, as shown below, have been thought for possible location of DSI Snake High Angle Conveyor system to transport coal from Kargali seam.
In this alternative HAC (DSI Snake High Angle Conveyor) shall be located towards internal dump. HAC shall be installed over the settled internal dump. Skid mounted in-pit crusher shall be installed in a suitable location at pit-bottom at RL 100.00 m level. An truck unloading platform shall be made by levelling the existing dump, so that trucks from coal benches can approach the unloading platform without any difficulties & un-load coal in the hopper of the in-pit crusher.
The crusher unit shall be provided with one internal grizzly within hopper to by-pass fine coals. (-) 600 mm size coal shall be discharged to roll crusher through apron feeder. The oversize lumps (+) 600 mm shall remain over another grizzly at top for breaking manually. The output from crusher shall be (-) 100mm & shall discharge on to DSI Snake High Angle Conveyor (HAC) by an integrated take-away conveyor fitted below crusher & one short bench conveyor. The entire crushing unit shall be skid mounted for easy installation at site & also shifting within pit, if required.
The HAC shall elevate (-) 100 mm size coal from RL +100.00 m level to a transfer hopper which shall be located in the dumble area by the side of existing road. The level at this point is around RL +238.00 m. The discharge drum of HAC shall be raised by another 8 to 10 m to discharge on to transfer hopper. The level may be RL + 248.00 m. That means the HAC shall negotiate a height of around 150 m. An overland conveyor shall collect coal below transfer hopper & shall carry directly from the transfer hopper to the washery. The overland conveyor (OLC) shall be installed onr structures with gantry keeping 8.0 m clearance from surface, so that there will be no interference with truck movements on the existing road.
In this alternative, the HAC shall be located just in the opposite side of Alt 1 & shall be installed over the existing sidewall of the mine, where mine has come to an end. In-pit crusher shall be located at pit- bottom in a suitable location in relation with the HAC. In this alternative, coal shall be disharged by HAC on to existing coal stock heap at surface. Washery shall be far from this location. Coal shall have to be transported by trucks from stock yard to either washery or to railway siding, as per existing system.
The alternative 2 shall be cheaper than alternative 1, since, this alternative shall not have any additional overland conveyor system. However, we have selected alternative 1& calculated economics, since, this is a complete solution & shall totally eliminate truck transport.
The detailed layout of integrated system with in-pit crushing system, DSI Snake HAC & overland conveyor are enclosed with this proposal vide drg. No.
|SYSTEM I:||Dumper transport from coal face to washery & crushing of coal at washery (Existing system)|
|SYSTEM II:||Dumper transport from coal face to in-pit crusher, HAC, OLC to washery|
|1. Annual production (MTPA)||1.00|
|2. Capacity of the system (TPH)||250.00|
|3. Annual operating hours (Hrs)||4,000.00|
|4. Lead distance of dumper (one way) from coal face to coal washery (SYSTEM I) (kM)||3.0|
|5. Lead distance (estimated) of dumper (one way) from coal face to in-pit crushing station for SYSTEM II (kM)||1.0|
|6. Estimated truck transport cost (Rs/Te) from face to in-pit crusher (SYSTEM II)||10.00|
|7. Dumper capacity (Te) 16 16. Existing contract rate for transport of coal from coal face to washery (SYSTEM I) (Rs/Te)||85.00|
|8. No. of skid mounted in-pit crusher||1|
|9. Length of HAC (meter)||200.00|
|10. Width of HAC & overland conveyor (millimeter)||1000|
|11. Annual discount rate (%) (for NPV calculation)||10.00|
|12. Annual escalation rate (%) (for DCF calculation)||4.00|
|13. Bank interest (%)||10.00|
|14. Life of project (Years)||15|
|15. Crushing cost for SYSTEM I (assumed) (Rs/Te)||5.00|
|16. Total manpower including operation & maintenance for SYSTEM II (for 3 shifts)||24|
|17. Annual salary & wage per person (Rs)||300000|
|18. Increase in contract price every fourth year (assumed)||10.00%|
|19. Electric unit price (Rs)||6.00|
Detailed economic analysis have been made for both SYSTEM I & SYSTEM II & relevant output charts/graphs are enclosed. The analysis has been done with our special MINE OPTIMISATION PROGRAM.
The following economic evolutions have been made:
The output results of analysis establish very attractive results in favor of SYSTEM II. The economic analysis has been made for annual production of 1.0 MTPA, considering 250 TPH system capacity with annual working hours of 4000 hrs. Since, the HAC system, in-pit crusher & overland conveyor, selected, are capable to handle 300 TPH without any additional investment, hence, economic analysis have been carried out with three options as follows:
From the analysis it may be observed that the opex shall be reduced for SYSTEM II with the increase of production, and there shall be no increase in capex. Hence, increase in production shall lead to better NPV, DCF, IRR & PAY BACK for SYSTEM II. All the comparisons relating to OPEX, NPV, DCF, IRR & PAY BACK for Options 1, 2 & 3 are included in this report. The relevant calculations, tables, charts & graphs are enclosed with this report as Annexures 1 to 8.
TOTAL POWER REQUIREMENT FOR SYSTEM II shall be 450 kW
|SYSTEM - I||SYSTEM - II||SAVINGS IN COST FOR SYSTEM II||ANNUAL NET SAVINGS||ANNUAL PRODUCTION (MTPA)||DISCOUNT RATE FOR NPV|
|YEAR||CAPITAL INVESTMENT (MINR) FOR SYSTEM - II||OPERATING COST (Rs/Te)||OPERATING COST (Rs/Te)||COST/TE (INR)||MINR||1.00||10%|
|NET PROFIT (MINR)||804.38|
|NPV (MINR) @ 10%||504.06|
|PAY BACK PERIOD (YRS)||4.47|
|DCF||475.13||DCF HAS BEEN CALCULATED CONSIDERING BOTH NPV & ESCALATION PER YEAR|
|Opt 1||Opt 2||Opt 3|
|CAPITAL INVESTMENT (MINR) (SYSTEM II)||248.80||248.80||248.80|
|NET PROFIT (MINR)||NET PROFIT (MINR)||1540.48||2515.31|
|PAY BACK PERIOD (YRS)||4.47||3.22||2.46|
|PRODUCTION (MTPA)||SYSTEM I (Rs/Te)||SYSTEM II (Rs/Te)|
1. From the economic analysis it is evident that coal transport by proposed System II with in-pit crushing & DSI Snake High Angle from Kargali seam pit-bottom to washery shall be quite profitable and shall save present dumper transport cost to a great extent. The capital investment for SYSTEM II shall be paid back in less than 5 years, whereas mine life is 15 years.
2. There shall be provision to increase production from 1.0 MTPA to 1.5 MTPA without any further capital investment. For increasing production present dumper system (SYSTEM I) shall be costlier, whereas SYSTEM II shall be cheaper. This shall further improve IRR of the project & shall bring down the pay back period to less than 3 years. Over & above, increase production shall lead to more revenue.
3. The DSI High Angle Conveyor shall be pollution free out of dust and exhaust fumes from trucks. The system shall satisfy the present norms of environment & pollution in mine.
4. The system shall be very safe & free from safety hazards of trucks, especially due to steep gradient in the mine.
DSI Snake High Angle Conveyor had been introduced in USA in 80’s & few hundreds of installations had been installed in several countries & have been running very successfully.
A reference list of High Angle Conveyor indicating locations & brief specification is enclosed. Currently DSI Snake High Angle Conveyor has attained capacity of more than 10,000 tph with 3000 mm Belt Width.