Introduction
Open pit mines are the principal source of minerals, soft coal and lignite throughout the world. Open pit mining methods are and promise to remain the economical mining method for the future.
Traditionally trucks have been the primary haulage means in open pit mines. It has been acknowledged generally that conveyor systems are more economical for transporting and dumping mined materials at very high volumetric rates. Such systems have been and are used in conjunction with continuous mining machines, such as bucket wheel and bucket chain excavators, in the lignite fields of Germany and in other parts of the world. These have been generally limited to application in soft or unconsolidated materials which will not consistently result in large boulders deposited on the conveyor belts.
Mining of hard rock and unconsolidated materials throughout the world typically involves blasting of the bank, loading by discontinuous means such as shovels, backhoes, front end loaders, etc., and haulage to the plant and waste dumps by large off-highway trucks in the 73 to 200 t (80 to 220 T) payload category. The many large boulders which result after blasting make continuous belt haulage impractical without further reduction of the material.
Truck systems offer flexibility in the mining operation because each truck can be rerouted on an hourly basis. Truck haulage costs have, however, increased steadily over the last two decades and dramatically in the late 1970s through 1980.
Unit capital and operating costs have increased due to inflation, the rapid increase in crude oil related commodities such as fuel, lubricants and tires, and due to increased pit depths which result in lowered truck efficiency and availability [1]. The truck fleet sizes are continually increasing due to increasing waste to ore ratios, decreased ore grades, increased haulage lengths and lifts as mines expand and deepen. Large support facilities, equipment, and maintenance crews are required to service the truck fleet and to construct and maintain large haulage ramps. Truck haulage costs now comprise as much as 50% of the total mine operating costs in some mines [2].
In response to increasing truck haulage costs and in the face of increasing tonnages to be moved, two large, U.S. copper mines, 181 to 227 kt/d (200,000-250,000 Tpd), 230 to 300 m (750-1,000 ft) deep [1, 3], responded in the late 1960s by installing high-capacity belt conveyors with large permanent type gyratory in-pit crushers. The in-pit crushers serve to reduce large boulders to conveyable size. These systems did not seek to eliminate all trucks, but rather to displace them by belt conveying, in elevating the ore and waste from within the pit and to the plant and waste dumps. In each case the flexibility of a trucking system was maintained within the pit from the mine face to the in-pit crusher.
These systems proved more economical than the truck only systems [1, 3], and the loss in overall mine flexibility was not initially a problem because of the local in-pit truck haulage. As the mines continued to expand and deepen, however, truck haulage costs once again began to climb due to the increased haulage lengths and lifts to the in-pit crushers. Permanent crusher locations were also found to obstruct the recovery of newly discovered ore and of material which had been reclassified as ore due to lowering of the cut-off grade. It was evident that the next generation of large crushers and conveying systems must provide for economical relocation of the system components to follow and not to dictate nor obstruct the direction of mining.
Mobile crushers with theoretical rates of 300 to 1,000 t/h (331 to 1,102 Tph) have been used to reduce material to conveyable size for over twenty-five years [4]. Only a few larger units have outputs of 1,000 to 1,600 t/h (1,102 to 1,754 Tph), and application has been predominantly in limestone.
High capacity mobile or movable crushers to reduce hard rock materials have only recently been developed. The U.S. Bureau of Mines (USBM) conducted a study from August of 1979 to November of 1980 which ultimately led to the design of a movable crushing system employing a large 1.52 – 2.26 m (60 – 89 in) gyratory crusher with a throughput capacity of 3,629 t/h (4,000 Tph) [5]. The crushing system which consists of separate self-contained crusher unit, apron feeder, and truck loading hopper can be moved once every year to once every two years by independent crawler type transporter units. Industry, too, has introduced several developments of similar movable crushing systems to feed movable and shiftable high-capacity belt conveyors [6, 7]. Such systems retain the local flexibility of truck haulage from the mine face to the hopper. The remaining material haulage is by conventional or high angle elevating conveyors to the pit perimeter and overland conveyors to the ore stockpiles and waste dumps, with waste spreading by shiftable conveyors and crawler mounted mobile stackers. Overall mining flexibility is also retained because all conveyors are either shiftable or movable.
Duval Corporation began installation of the first movable in-pit crushing and conveying of this kind in 1981 at its Sierrita copper and molybdenum mine near Tucson, Arizona. Operation began in December 1982, and plans were made immediately for two duplicate systems at the same property [7]. Present world market conditions have delayed implementation of these plans. Operation of another similar system also began in 1982 at Sishen’s North iron ore mine in South Africa [8]. Many other companies throughout the world are now in various stages of implementing such systems. Most notable among these is the Majdanpek Copper Mine in Yugoslavia [12, 15]. It will install an ore haulage system for operation in 1988, which will use portable in-pit crushers and movable conveyors and a high angle conveyor (HAC®) for elevating the ore to an out-of-pit conveyor system to the concentrator.
Completely self-contained and self-propelled mobile gyratory crushers, highly mobile connecting conveyors, shiftable conveyors, and stackers were also installed in a South African coal mine to reduce and transport shovel loaded overburden at 3,000 t/h (3,307 Tph) design rate to the out-of-pit waste dumps. This system has completely eliminated truck haulage [9]. Highly mobile high capacity crushing and conveying systems for coal are also possible with high-capacity crawler mounted feeder breakers [10] and roll crushers.
Since the installation of the first large in-pit crushing and conveying systems, the trend had moved slowly towards more mobile and, therefore, more flexible crushing and conveying systems. Movable, shiftable and mobile conveyors had significantly improved overall system flexibility. The vital link which permits optimization of any in-pit conveying system, however, had until now been missing.
HAC® is a Key to Efficient In-pit Crushing and Conveying
The ore haulage system at Majdanpek copper mine will be the first to introduce this vital system, a high-capacity high angle conveyor (HAC®) which meets the performance requirements of hard rock open pit mines. HAC® systems offer many advantages over traditional truck haulage systems including:
Superior Energy Efficiency
Trucks must transport their own dead load in addition to the payload. Dead load can range up to 45% of the gross hauled weight when the truck is loaded to capacity. In a high angle conveyor, the energy goes towards elevating material with only a small amount lost to idler and pulley friction, material acceleration, etc.
Less Dependency on Petroleum Products
Electrical power for a high angle conveyor system is increasingly generated by coal, hydro, and nuclear power. The dependency on imported oil and the prospect of diesel fuel rationing need not concern the mine planner.
Less Sensitive to Inflation
A high angle conveyor will have a longer life and much lower maintenance costs when compared to trucks which are replaced every six to eight years.
Less Labour Cost
A HAC system requires less operators, maintenance personnel and facilities. Trucks require one driver per shift each, and large maintenance crews must provide continuous upkeep and repair to keep the truck fleet operating.
Less Total Excavation
High angle conveyors may be supported along any stable slope. Total excavation is, therefore, determined by geotechnical stability considerations and not by the 8% to 10% maximum slope requirements of the truck haulage ramps. This also makes a high angle conveyor superior to a conventional elevating conveyor with maximum slope of 27%.
Less Haulage Road Maintenance
A high angle conveyor system requires only small access roads for maintenance vehicles. This greatly reduces the large equipment fleet and thus costs required for large truck haulage ramps.
COMPANY |
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Demonstration Unit Data | Triton Coal Company | Majdanpek Copper Mine, Yugoslavia | Western USA Company | |
Materials conveyed | Lignite, coal, copper ore and waste rock, iron ore pellets, sand, gravel, grain | Coal | Copper ore | Coal |
Density, t/m3 | 0.8 – 2.4 | 0.8 | 2.08 | 0.8 |
Lump size, mm | Up to 229 | 51 | 250 | 51 |
Conveyor angle, degrees | 30 to 60 | 60 | 35.5 | 35 |
Conveying rate, t/h design | 1955 – coal
2468 – rock 2684 – iron ore |
1814 | 4000 | 2903 |
Surge | n/a | 1996 | n/a | n/a |
Belt width, m | 1.524 | 1.524 | 2.00 | 1.829 |
Belt speed, m/s | 0 to 6.1 | 4.65 | 2.67 | 4.57 |
Elevating height, m | 7.9 to 19.5 | 32.9 | 93.5 | 29.0 |
HAC conveyor drives | ||||
Top belt, kW | 75 | 112 | 450 | 149 |
Bottom belt, kW | 112 | 149 | 900 | 224 |
Ore Haulage System at Majdanpek Copper Mine
Majdanpek copper mine began to exploit the favorable economics of crushing and conveying by startup, in 1983, of a continuous haulage system.
This system uses two fixed, adjacent crushing stations at the pit perimeter to feed a common 6,000 t/h 1.2 km long conveyor to the waste dump where a 8,000 t/h, 1,3 km long, slewing, shiftable conveyor with tripper transfers the material onto a crawler mounted stacker. Haulage from pit to crushers is by 170 and 200 T end dumps.
It is only natural to further exploit the economic advantages of conveyorized haulage at the ore. Because of proven performance of the waste haulage system and timeliness due to increasing pit depth, a study began immediately in 1983 into an in-pit crushing and conveying system for the ore.
The study was especially timely with regard to available technology. As mentioned previously, by 1983, large portable in-pit gyratory crushers had been installed at a large porphyry type copper mine in the U.S. and at a large iron ore mine in South Africa. The flexibility, high throughput and ruggedness of this type crushing plant is considered crucial since past installation of fixed in-pit crushing stations has proven constraining to mine operation.
By 1983 the high angle conveyor-HAC®, an equally important technology, had been developed and tested on a large-scale prototype (Table 1 and Fig. 1). By early 1984 the HAC had reached commercialization by installation of the Triton-HAC® (Table 1, Fig. 2) in Wyoming, USA. Using the HAC® as the elevating means permits the most direct path out of an open pit mine while minimizing obstruction and excavation at the wall.
Fig. 3 illustrates the planned in-pit crushing and high angle conveying system to begin operation at Majdanpek in 1988. Fig. 4 is a 1986 photo of the Majdanpek pit with an artist’s sketch of the HAC®, superimposed. This system uses the latest in technology and will no doubt serve as a model for the future in hard rock mining. The two existing 1.2- 1.9 m (48-74 in) gyratory crushers will be made portable and relocated within the pit. With a 250 mm open side setting these are capable of a combined 4,000 t/h crushing rate. Movable in-pit conveyors 1,200 mm wide, running at 3.8 m/s are the link between the crushers and the high angle conveyor at the pit wall. A 2,000 mm wide HAC (Table 1 and Fig. 5) elevates the material 93.5 m, at 35.5°, out of the pit onto a 1,200 mm wide overland conveyor, leading to the existing ore conveyor between the present primary and the secondary ore crushers.
Majdanpek’s desire to permanently locate the HAC® results in early scheduling of local excavation toward the ultimate pit wall at the southwestern end of the pit. This does not represent additional total excavation but rather an earlier scheduling. Early concepts considered pontoon mounting of the HAC® for portability compatible with the in-pit crushers
Demonstration Unit Data | Triton Coal Company | Majdanpek Copper Mine, Yugoslavia | Western USA Company | |
Materials conveyed | Lignite, coal, copper ore and waste rock, iron ore pellets, sand, gravel, grain | Coal | Copper Ore | Coal |
Density, pcf | 50 to 150 | 50 | 130 | 50 |
Lump size, inches | Up to 9 | 2 | 10 | 2 |
Conveyor angle, degrees | 30 to 60 | 60 | 35.5 | 35 |
Conveying rate, STPH | ||||
Design | 2155 – coal | 2000 | 4409 | 3200 |
2721 – rock | ||||
2959 – iron ore | ||||
Surge | n/a | 2200 | n/a | n/a |
Belt width, in. | 60 | 60 | 78.7 | 72 |
Belt speed, fpm | 0-1200 | 915 | 525 | 900 |
Elevating height, ft. | 26-64 | 108 | 307 | 95 |
HAC conveyor drives | ||||
Top belt, HP | 100 | 150 | 600 | 200 |
Bottom belt, HP | 150 | 200 | 1200 | 300 |
and conveyors. The ideas were ultimately discarded in favor of the present arrangement.
Fig. 3 shows only one arrangement of the open pit system. The portable crushers and movable conveyors have the flexibility to follow the progress of mining, and the configuration will change from year to year with all ore flow leading to the HAC. As the pit continues to deepen, a second HAC will be installed at a lower elevation to dump onto the first.
The portable crushers and movable conveyors will be relocated to optimize the in-pit haulage by end dump trucks. The present 170 and 200T haulers are now being replaced by even larger 220 Tend dumps and only the 220 T payload units are expected to be in operation by 1988.
In-house studies by Majdanpek engineers project accumulated savings of $ 142,000,000 (1986 U.S.$) by year 2002, due to the in-pit crushing/HAC® in lieu of a truck only haulage system.
High Angle Conveyor – HAC®
HAC® Development
Development of the Continental HAC® began with studies in 1979. These ultimately led to the decision in 1982 to design, build and test the first large scale HAC® unit. Such a prototype (Table 1 and Fig. 1) was operational by mid 1983 and testing of performance with various materials, including copper ore and waste, began immediately. The Majdanpek personnel were able to visit Winfield, Alabama, USA, the site of the prototype unit, on various occasions to witness the HAC in operation under conditions which simulate the Majdanpek Mine operation. The unit has to date performed many such demonstrations for various industries.
The first commercial order for a Continental HAC® came within six months of the prototype’s first operation. It was delivered to Triton Coal Company in Wyoming (Table 2 and Fig. 2) by April 1984 with start-up in May. The Majdanpek HAC® (Table 1 and Fig. 5) represents the second commercial order, but a third HAC® order is already in the final stages of engineering and will be operational at a coal mine in Wyoming USA (Table 1 and Fig. 6) by November of 1986.
The Sandwich Belt Principle
The Continental HAC® represents evolution to the latest state-of-the-art in sandwich belt high angle conveying. The sandwich belt approach employs ordinary rubber belts which sandwich the conveyed material. Additional force on the belts provides hugging pressure to the conveyed material in order to develop sufficient friction at the material to belt inferface so that sliding back will not occur at the designed conveying angle. Fig. 7 is a simplified illustration of the interaction of forces. If the cover belt is not driven, the lineal force N provides the required hugging pressure at conveying angle α as given by the following equation:
( )
where µ = µm or µ = µb, whichever is smaller.
A more realistic model is shown in Fig. 8. An ample belt edge distance assures a sealed material package during operation even when belt misalignment occurs. A more comprehensive treatment of force interaction for a complex model along with the implications of driving both belts is not within the present scope and can be found in Dos Santos and Frizzell [11, 14].
The Continental HAC consists of a carrying conveyor belt which is supported on closely spaced troughing idlers and a floating cover belt which is softly pressed onto the conveyed material by closely spaced, fully equalized, pressing rolls. The required material hugging pressure varies according to the conveying angle, material characteristics and the dynamics of the system. The hugging pressure device is, therefore, designed for the specific requirements of the application with provision for field adjustment.
Advantages of Continental Conveyor Sandwich Belt HAC®
The Continental Conveyor HACs can take on various forms as illustrated in Figs. 9-13, and offer many advantages over other systems including:
Simplicity of Approach
The use of all conventional conveyor hardware means interchangeability of components, and fast delivery of replacement parts. Operating experience with conventional conveyors leads us to expect high availability and low maintenance costs.
Virtually Unlimited in Capacity
The use of conventional conveyor components permits high conveying speeds. Available belts and hardware to 3 m (120 in) wide make possible capacities greater than 13,608 t/h (15,000 Tph).
High Lifts and High Conveying Angles
Lifts to 107 m (350 ft) are possible with standard fabric belts and single run lifts greater than 305 m (1000 ft) are possible with steel cord belts. High angles to 90° are possible without excessive wear because of the soft, floating, fully equalized hugging pressure device.
Flexibility in Planning and in Operation (see Figs. 9-13)
The Continental Conveyor sandwich belt lends itself to a multi-module conveying system using self-contained units as well as to a single run system using an externally anchored, high angle conveyor. In either case, the conveyor unit may be shortened or lengthened, or the conveying angle may be altered according to the requirements of a new location. High angle conveying modules may be mounted on rails, rubber tires or crawler type transporters or may be equipped with walking feet for optimal mobility.
Belts are Easily Cleaned and Quickly Repaired
Smooth surfaced belts allow continuous cleaning belt scrapers or plows. This is especially important in handling wet and sticky material. Smooth surfaced belts present no obstruction to quick repair of a damaged belt by hot or cold vulcanizing. Quick repair means less costly downtime.
Spillage Free Operation
During operation, the material is sealed between the carrying and the cover belts. Well centered loading and ample belt edge distance results in no spillage along the conveyor length.
HAC Systems Application in Open Pit Mining
Each form of the HAC unit, as illustrated by Figs. 10-13, is especially suited for the mobility, flexibility, lift and tonnage requirements of particular types of open pit mining operations.
The resulting HAC systems may take many forms. As a minimum, any HAC system consists of: (1) an in-pit crushing system to reduce material to a conveyable size, (2) the HAC to elevate material out of the pit, and (3) an out-of-pit conveying system to take the material to the plant or to the waste dumps. The following describes some of the many possible HAC systems.
Deep Open Pit Mines
Multi HAC units may be arranged in series (see Figs. 10 and 14), with the lower HAC module discharging onto the upper HAC to achieve high lifts from deep open pit copper, taconite, or phosphate mines. The system of Fig. 14 consists of truck haulage from the mine face to an in-pit movable crushing system, the movable crusher, one or more HAC units, and an out-of-pit conveying and tail ends to relieve the intermediate support spans of the belt tension forces. A long transition curve from the HAC loading area to the ultimate conveying angle is also required with a troughed steel cord or aramid fibre belt, because of the high axial stiffness of the reinforcement. The result is a less mobile HAC system with increased imposition into the pit because of the long transition curve. A single run HAC will be less expensive, however, and the elimination of material transfer points will improve the system’s availability.
Thin Seam Strip Mines
The highly mobile HAC unit of Figs. 12 and 16 eliminates the need for trucks and haulage ramps traditionally required to haul coal out of single or multiple thin seam strip mines. The HAC system is used to convey from pit to plant with primary overburden stripping by dragline in direct cast or extended bench mode. Pre benching and recontouring may be by other means, such as bucket wheel excavators with end around conveyors and stackers, by scrapers, or by shovels and trucks. Coal loading into the mobile crusher may be by shovel, backhoe, or front-end loader. Continuous excavating machines, such as bucket wheel excavators or easy miners may also be used to load the coal directly onto the HAC without the need for additional crushing.
The HAC system consists of a mobile crawler mounted high-capacity feeder breaker or roll crusher to reduce the lump size, a mobile crawler mounted HAC unit to elevate coal from within the pit, a crawler mounted beltwagon, a shiftable conveyor, and an overland conveyor to take the coal to the plant (overland conveyor is not shown in Fig. 16).
The present HAC unit is ideally suited to work with large stripping draglines, because of its high mobility and the single bench suspension. This makes possible continuous travel along an irregular dragline bench and around the dragline cut when the HAC and dragline must cross each other’s path.
Depending on the overburden thickness and the size of the stripping dragline, the HAC unit may have a lift of 18.3 to 36.6 m (60 to 120 ft). Depending on the bank stability, the conveying angle may be 45° ta 60°. Design rate for the mobile crusher, HAC, and the other conveyors is in the range of 907 to 1,814 t/h (1,000 to 2,000 Tph). Mobility must be continuous for the mobile crusher, HAC, and connecting beltwagon since they follow the continuous advance of the dragline cut. Frequency of shiftable conveyor advance depends on the advance distance, pit length, overburden thickness and production rate of the dragline. This may be from once every several weeks to once every several months. The overland conveyor is lengthened at the tail end in 152 to 305 m (500 to 1,000 ft) increments or once every several months.
The mobile feeder breaker or crusher must reduce the coal to 152 to 254 mm (6 to 10 in) maximum lump size depending on the design rate, belt width, etc. Such a crusher must be equipped with a luffing, swivel, discharge boom of ample length to permit easy loading of the HAC even when the dragline bench height varies slightly along the pit length.
Thick Seam Mines
Very thick seams, up to 42.7 m (140 ft) of sub-bituminous coal are presently mined in the western U.S. by shovel truck open pit methods. Overburden thickness, initially 12.2 to 18.3 m (40 to 60 ft) will increase to approximately 91.4 m (300 ft) before end of mine life in some cases. This makes necessary multiple benches in the overburden with one to three thick benches in the coal seam. Such requirements make the HAC configuration of Figs. 13 and 17 most appropriate. The HAC® system is again used to convey the coal from pit to plant. Overburden removal and spoiling may be by bucket wheel excavators with end around conveyors and stackers, by scrapers, or by shovels and trucks. Coal loading into the mobile crusher may be by shovel, backhoe or front-end loader.
The HAC system consists of one or more mobile crawler mounted high-capacity feeder breakers or roll type crushers, each with crawler mounted beltwagon, an in-pit shiftable conveyor with hopper cars as required, an HAC with connecting conveyor bridge and loading hopper car, and an overland conveyor to the plant. In a three-bench operation, the single in-pit shiftable conveyor must be located on top of the middle bench with long beltwagons or bench type high angle conveyors feeding the coal from the lower and upper benches. In-pit shiftable conveyors may be employed at two or more coal benches for system redundancy and to minimize conveying between benches. This, of course, requires as many HAC units as there are shiftable conveyors.
A multiple bench operation makes impossible a single HAC lift out of the pit at the advancing high wall. Such a single lift can only be at the end wall where the multiple benches come together as two or three very high non-advancing benches. The HAC units consist of the HAC, a conveyor bridge, and a hopper car. The HAC has lower support within the pit and an upper support at a strategic elevation with regard to the ultimate thickness and variation of the coal seam and overburden. The conventional conveyor bridge spans the HAC and overland conveyor, changing its angle to lower or elevate the material as required by the varying total elevating height. A rail mounted hopper car. supports the discharge end of the conveyor bridge and directs the coal onto the overland conveyor. The HAC with support at two bench elevations spans an intermediate bench which can be used for pit access, truck haulage, or conveying the overburden to the spoil side of the pit.
HAC lift requirements may be from 36.6 to 76.2 m (120 to 250 ft) with combined HAC and conveyor bridge unit from 45.7 to 91.4 m (150 to 300 ft). The HAC conveying angle is approximately 45°, while the conveyor bridge is limited to + 15°. Design rate for the mobile crushers and beltwagons will match the maximum production of a 30.6 m® (40 yd) shovel at 2,722 t/h (3,000 Tph). Each shiftable conveyor and HAC unit are designed for 2,722 t/h (3,000 Tph), 3,629 t/h (4,000 Tph), or 5,443 t/h (6,000 Tph) depending on whether these are carrying the production of one, two or three coal loading shovels. The overland conveyor is designed for 3,629 t/h (4,000 Tph) or 5,443 t/h (6,000 Tph). Mobility must be continuous for the mobile crushers and belt wagons since they follow the advance of the bench cut along the entire pit length. These are, therefore, permanently mounted on self-propelled crawlers. The frequency of advance for the shiftable conveyor and the HAC unit along the endwall depends on the advance distance, pit length, coal thickness and production rate. This may be from once a month to once every several months, and this does not warrant permanently attached transport means. The HAC unit is, therefore, mounted on pontoons at the lower and upper ends with provisions for transport by rubber tired or crawler mounted independent transporter units, or by attachable/detachable walking feet. Whichever transport means chosen will also be used at the drive and tail stations of the shiftable and overland conveyors. The tail end of the connecting conveyor bridge is supported on the HAC structure while the discharge end is supported on a rail mounted hopper car which is not self propelled and must be towed during the advance of the HAC. Extension of the overland conveyor may be in 151 to 305 m (500 to 1,000 ft) increments or once every several months.
The mobile feeder breaker or crusher for this application must be equipped with luffing, swivel discharge boom as in the thin coal seam strip mine applications.
Fig. 18 illustrates another form of the HAC system in thick seam coal mining. The approach is similar to the thin coal seam system of Fig. 16 except the shiftable conveyor trails on a prepared spoil bench rather than advancing on the prepared dragline bench. The mobility requirements are similar to the thin coal seam system, while the design rates for the highly mobile HAC, the connecting beltwagons, shiftable conveyor and overland conveyor are much higher at 2,722 to 3,629 t/h (3,000 to 4,000 Tph). The HAC lift is approximately 30.5 to 45.7 m (100 to 150 ft), and the conveying angle may be 30° to 40° depending on the stability of the spoil material. In this scheme, much of the stripped overburden is spoiled in the mined out pit to form a prepared bench for the HAC and shiftable conveyor. This requires much spreading by dozers after dumping. The remaining overburden is spoiled behind the shiftable conveyor and can, therefore, be contoured and seeded according to reclamation requirements.
Multiple Thin Seam Mine With Thick Parting
The HAC® system of Fig. 19 illustrates the use of both a highly mobile HAC at the highwall and a movable HAC unit with connecting bridge and hopper car at the end wall. The characteristics of the mobile crushers, beltwagons and highwall HAC are as described in the thin coal seam system of Fig. 16 while the shiftable conveyor, end wall HAC unit and overland conveyor are as described in the first thick coal seam system of Fig. 17.
HAC® Bench Conveyors
Pontoon, crawler, or rubber tire mounted HAC bench conveyor for 10.7 to 15.2 m (35 to 50 ft) bench heights may be used with beltwagons, crawler mounted self-aligning face conveyor, and/or cascading conveyor modules to produce a highly mobile, highly flexible, haulage system which can be used locally to advance one or several overburden benches to uncover a desired amount of ore. The system can then be removed and relocated for operation in another area of the mine or at another nearby mine. Such a system requires that all components be highly mobile or of a size and mass that makes them easily towed by other mine equipment or lifted by mobile crane. With a projected operating mass in the 18.1 to 36.3 t (20 to 40 T) range, the HAC bench conveyor qualifies for the latter.
Summary and Conclusions
There are serious doubts about the future viability of trucks as the primary means of material transport in open pit mines. Two large U.S. copper mines realized large cost savings by installing permanent type large gyratory crushers and conveyors to displace trucks in elevating material from within the pit. These had the disadvantage of reducing mining flexibility and limiting the amount of ore recovered. The introduction of large movable gyratory type in-pit crushing systems, and movable and shiftable elevating and overland conveyors have improved the overall flexibility of the mining operation. The remaining disadvantage was that the conventional elevating conveyors must be routed along approximately 15° conveying angles. This did not permit optimal mine slope angles, and additional excavation was required to accommodate the low angle conveyors. The high angle conveyor (HAC) is, therefore, the key to system optimization when used as the continuous elevating means. Majdanpek copper mine in Yugoslavia is the first to exploit the advantages of an in-pit HAC system.
Studies had revealed the economic advantages of HAC systems in open pit mining. Past state-of-the-art searches, however, found no high angle conveying method to meet the requirentents of large open pit mines. This need has been filled by the development of Continental Conveyor HACs and HAC systems. Various forms of these have been discussed, and several applications in open pit mining have been illustrated. HAC development has advanced well into the commercial stage and the advantages of the HAC systems described can now be exploited with great confidence in the proven performance of all systems components.
References
[1] Coile, J.J., “In-Pit Crushing and Conveying vs Truck Haulage”, Mining Congress Journal. Vol. 60, No. 1, pp. 23-27, January 1974.
[2] Mevissen, E.A., Siminerio, A.C., and Dos Santos, J-A., “High Angle Conveyor Study”, by Dravo Corporation for Bureau of Mines, U.S. Department of the Interior under BuMines Contract No. JO295002. Volumel, 291 pages, Volume ll, 276 pages. 1981.
[3] “Pit Crushers and Conveyors Move Sierrita Ore and Waste”, Engineering and Mining Journal. Vol. 178, No. 6, pp. 102-103, June, 1977.
[4] Kok, H.G., “Use of Mobile Crushers in the Minerals Industry”, Mining Engineering. Vol. 34, No. 11, pp. 1584-1588, November, 1982.
[5] Almond, R.M. and Schwalm, R.J., “In-Pit Movable Crushing/Conveying Systems”. Mountain States Mineral Enterprises, Inc., presented at the AMC International Mining Show, Las Vegas, Nevada, October 11-14, 1982.
[7] Iles, C.D., “Cost of In-Pit Crushing”, Mining Engineering. Vol, 35, No. 4, pp. 319-320, April 1983.
[8] . “Iscor’s Sishen Grows and Grows”, Engineering and Mining Journal. Vol. 183, No. 11, pp. 122-125, November, 1982.
[9] Alberts, B.C. and Dippenaar, A.P., “An In-Pit Crusher Overburden Stripping System for Grootge-luk Coal Mine”. South African Institution of Mechanical Engineers, One Day Symposium on Materials Handling in Opencast Mining, September 18, 1980, 21 pages.
[10] “Feeder Breakers”, Mining Magazine. Vol. 146, No. 2, pp. 149-155, February, 1982.
[11] Dos Santos, J.A. and Frizzell, E.M., “Evolution of Sandwich Belt High-Angle Conveyors”, C/M Builetin. Vol. 576, No. 855, pp. 51-66, July, 1983.
[12] Reisler, N. and Stanisic, Z., “Converting to Conveyors,” Engineering and Mining Journal. Vol. 182, No. 10, pp. 106-108, October, 1981.
[13] Dos Santos, J.A., “Sandwich Belt High Angle Conveyors-Applications in Open Pit Mining”, Bulk Solids Handling, Vol. 4, No. 1, pp. 67-77, March 1984.
[14] Dos Santos, J.A., “Sandwich Belt High Angle Conveyors – HAC Evolution to Date”, Bulk Solids Handling, Vol. 6, No. 2, pp. 299-314, April 1986.
[15] Dos Santos, J.A. and Stanisic, Z., “In-Pit Crushing and High Angle Conveying in Yugoslavian Copper Mine”, for presentation at Mining Latin America, International Mining Convention in Santiago, Chile, November 17-21, 1986.
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