Hlobane Colliery SYNOPSIS

Transcription

1 Low-Seam Auger Mining R E COLLINS The Vryheid (Natal) Railway, Coal Hlobane Colliery Hlobane Colliery Iron Co. SYNOPSIS H lobane Colliery operates a low-seam auger to extract reserves from outcropping coal seams which would not otherwise be mineable by underground methods. The auger machine is to drill circul-ar holes with a diameter of 500 mm to 700 mm, and with a length of hole of up to 70 m. The total seam recovery is 40 percent. A production rate of 1000 run-of-mine tons per month is the auger on a shift. The cost per ton compares very favourably with underground methods. INTRODUCTION Hlobane is situated some 28 km east of Vryheid in the Vryheid Magisterial District of Republic of South Africa. The Colliery is one of four mines owned by Iscor Limited which supply metallurgical coal to Iscor's steelworks. Production averages tons of run-of-mine (ROM) coal per month by continuous miner using the rib pillar extraction method, from drill and blast sections with both bord-anddevelopment and pillar and from a small opencast tion (contour mining) where coal in the highwall is extracted by The of the comes from underground, with ROM tons per month from the opencast and auger Owing to the shortage of good-quality coking coal reserves in South it is a policy of Iscor to maximise the extraction of the reserves at Hlobane. The reserves between the underground workings and the coal seam outcrop were identified as an area which could be mined to improve the overall extraction of the coal seams. Previous practice had been for the when the outcrop, to stop as soon as roof conditions began to deteriorate. Coal seams at the outcrop were mined in certain areas open cast where a favourable ratio existed. This resulted in a of coal left between the underground workings and the surface. It was not initially planned to mine these reserves. In 1984, an auger was from the United States of America for use at Natal Ammonium, a colliery. conditions at Natal Ammonium are similar to those at Hlobane, except that the coal seam mined at Natal Ammonium is thicker. The of an auger at Hlobane was confirmed by Hlobane personnel Natal Ammonium. Enquiries regarding a suitable machine to suit the low-seam conditions at

2 however, negative. Hlobane management therefore decided to fabricate an auger machine on the Col suitable for the low-seam conditions at the mine. It was also decided that the machine be for both surface and underground mining. Design and fabrication of the auger commenced in 1987 and was in October The machine was tested on surface and underground from October 1987 until June 1988, during which time certain modifications were made. Following the a decision was made not to use auger as an mining system due to the low percentage recovery of coal remaining in developed pillars. It was therefore decided to use the auger only on as in conventional augering Other more mining methods such as the were also evaluated. On 10 June 1988, the auger commenced production on a permanent basis from the high wall of a small contour The seam being extracted has an average thickness of 600 mm and the cutting head is 500 mm in diameter. Production rates have been fair with a maximum of 232 m (66 ROM tons) drilled in a single shift. The auger is presently worked on a permanent day but double shift will commence in September 1988 once suitable floodlighting arrangements have been made.

3 GEOLOGY The coal measures at Hlobane belong to the Vryheid Formation (Middle of the Ecca Group. The sediments consist of coarsegrained sandstones with some shale as shown in Figure I. Two major dolerite sills, the and Matshongo!olo, cap the Hlobane Mountain and create the characteristic in the area. The underlying coal seams outcrop around the sides of the mountain and access to the underground workings is generally by horizontal adits. The heating effect of the dolerite sills at the time of intrusion gave the coal seams their properties. The of the coal is poorer in the upper coal seams, which are closer to the dolerite sills. The coal measures consist of several seams, of which only four (the Upper Dundas and are of economic A general section of the coal seams is shown in 2. The Alfred Seam, 1,60 m thick, is now virtually mined out, with only a small reserve as The underlying Gus 17 m below the Alfred. has an average thickness of 980 mm. The Dundas Seam, 15 m below the Gus, has an average thickness of 1,5 m but contains a sandstone and shale intra-seam parting 600 mm thick. The bottom coal below the is 600 to 700 mm whereas the top coal above the has a thickness of only 200 to 300 mm. The Upper Dundas is mined locally, where the seam becomes thicker. At present the entire is from the Gus and Dundas seams, with 40 percent the Gus and the remainder from the Dundas. Due to a difference in the coal qualities, the two seams are not blended together but are beneficiated and despatched to the steelworks as separate The seams are generally flat-lying, but are divided into a number of blocks defined dyke-fault structures with throws of up to 27 m. Dolerite dykes, with associated minor displacements, occur in the workings. The are orientated generally in a northwest-southeast or northeastsouthwest as the Alfred Seam has been mined out, the and fault structures can be with reasonable accuracy on the plans of the underlying coal seams. In the the auger was used to extract the bottom coal of the Dundas Seam in developed at the full seam In the surface operations, the auger has been used on the Gus Seam and also on the bottom coal of the Dundas.

4 MIQ BASIC DESIGN PARAMETERS OF THE AUGER The auger was for both surface and operations. The dimensions of the developed roadways in the underground bord-andsevere restrictions on the overall size of the machine. It was determined that the auger had to be to operate in a roadway with a width of m and a height of 1,2 m. The basic parameters that the auger was required to meet are detailed as follows: size Maximum overall height Maximum length of machine base plate Maximum width of machine base plate Length of individual auger sections Diameter of cutting head (3 sizes to extraction of coal seams) Maximum length of auger hole 1,2 m 5,Om 4,Om 2,Om 500 mm, 600 mm and 700mm 70m The maximum of a scroll section could not exceed 2 m, owing to the confined space in the It was that the short scroll sections would increase deviation of the head, and have an adverse effect on directional control. A suitable coupling was to minimise the deviation between scroll sections. As Hlobane is classified as a all had to comply with the relevant South African Bureau of Standards and Government Mining for flame-proof equipment. TECHNICAL SPECIFICATIONS OF AUGER Following the underground and surface trials carried out between October 1987 and June 1988, certain modifications were made to the original machine. The machine was altered in accordance with the given below. The components of the auger are indicated in Dimensions machine of machine base plate Width of machine base m 2,Om Auger of individual auger sections - 2,Om Diameter of cutting head (3 sizes to 500 mm, 600 mm optimise extraction of coal and 700mm Pitch of auger spiral 500mm length of auger hole 70m Rotational speed 87 rpm A uger couplings Type with an angle of 10 Material used EN 19 condition T

5 Main electric molor Power Speed llokw 1440 rpm Voltage Type Main hydraulic pump Delivery pressure - Hydraulic molor - Power at maximum continuous speed Displacement output Speed Rotation - Secondaty electric molor Power - Flameproofing SecondOlY hydraulic pump Type Delivery pressure Speed Coal transport system First stage Second stage Third stage - ~ cycles Hall f per minute (two in parallel mounted on common shaft) 17 MPa 1440 rpm Staffa B kw 4,31 e per revolution 14 knm at 20 MPa Variable up to 125 rpm Hi-directional kw 1440 rpm Flameproof 380 V, 3 phase, 50 TEFC Hall e per minute I Mpa 1440 rpm Armoured flight conveyor Belt conveyor motor on armoured flight conveyor Type Motoridutorri, Series MR301 Power at maximum continuous 15kW Torque output - 0,588 e per revolution 114Nm at 15,5MPa - Variable up to 105 rpm Rotation Bi-directional 409

6 DESIGN OF CUTTING HEAD The criteria adopted in the design of a cutting head were to obtain: - Maximum penetration Minimum power - Minimum head deviation In order to satisfy the above requirements it was decided to a cutting head with a concave pick configuration. Much was placed on the calculations of lacing, spacing, cutting speeds, rake angles etc, but field tests showed that the specific energy required to obtain a reasonable was much beyond the of the machine. The head was redesigned and a convex type was built. It was found that by the rake to a minimum of 30 the specific energy and cutting forces were reduced considerably. In order to further reduce the energy consumed it was necessary to achieve optimum interaction between picks. The depth to ratio for minimum energy consumption was determined as shown in Figure 4. Some refinements were made after a series of trial tests were run. The final head is shown in 5. In order to minimise deviation the auger couplings had to be to achieve the r"'fn",r"ri rigidity with minimum coupling and decoupling t'ime. AUGER COUPLING The design of the auger coupling is shown in Figure 6. Since the auger sections were limited to a maximum of 2 m, and quick characteristics are of prime importance. Conical, male and female halves are used. The coupling and coupling pin are made from EN 19 material. The taper on the coupling is 10, as this was found most suitable to prevent self-locking and maintain rigidity. SLIDING DRIVE UNIT A general view of the drive unit is shown in 7. Owing to the large end thrusts, careful consideration had to be given to the of the shaft. A heavy duty plummer block arrangement, 8, was designed and manufactured for this application. UNDERGROUND TRIALS Underground trials were conducted in the Dundas Seam workings of M5untain Adit. The workings had been developed on a bord-and-pillar layout several years prior to the commencement of the trials. The adit was worked originally and tubs were transported an endless As the haulage was in good condition it was decided to make infrastructure rather than to install an extensive conveyor

7 were 5,0 m wide m the full of the Dundas Seam. A typical section of the Dundas in the area of the trials at Mountain Adit is shown in 9. It had been to mine the developed pillars to improve the overall extraction of the reserves. Pillar extraction (or 'stooping') has been practised at Hlobane for many years, allowing recovery of up to 85 percent of the coal within a as the Dundas contains a stone parting, a low mining yield is achieved when developing and extracting pillars at the full seam height. Past efforts to improve the mining yield by mining bottom coal and only a portion of the stone have met with little success, to excessive costs associated with stone 'and mechanical support The overall ROM yield at Hlobane Colliery is 36 percent and an improvement in the was seen as critical to the cost per sales ton. The auger was therefore to extract the bottom coal in l1pijpi{-,nf'l1 Dundas pillars to improve the yield of the ROM coal reporting to the beneficiation plant. At Mountain Adit the bottom coal has a thickness of 700 mm, and it was found that a cutting head with a diameter of 600 mm would maximise extraction without fouling the stone or floor. The pillars mined had a length of 25 m and a width of 16 m. As the depth of cover was only 45 m, the conditions for pillar extraction were considered to be good. The bottom coal was out in the manner shown in 3. Ribs of 200 mm were left between with 50 mm of coal left above and below the hole. The machine is moved along the face in the underground workings by means of and hydraulic anchor which are set the roof. Augered coal is loaded into tubs and out of the section on an endless rope haulage, which was already in existence at Mountain Adit prior to the trials. It was planned that should the trials prove the coal would be transported using a continuous conveyor system. Figure 10 shows the auger in operation in the underground section. In this the hydraulic motor is in a different to that on the machine now in use. No serious operating problems were experienced, although some holes were drilled short owing to rolls in the coal seam, which resulted in the head cutting into the floor or stone The results of the trials can be summarised as follows: 1. The auger achieved the objective of improving the mining A yield of 70 percent was achieved from the section, compared with 27 percent had the full seam been mined by conventional methods. 2. The cost per sales ton was good, very favourably with the other methods in use at Hlobane as below, ranked in order from the lowest in-section cost to the highest: 411

8 (1) Auger. (2) Fairchild Wilcox continuous miner. (3) Pillar extraction handloading methods. (4) Double-stall Bord-and-pillar mining gathering arm loaders into ba ttery tractor-trailers. (6) using ultra-low battery scoops. 3. Production the trials was poor, with only 300 tons shift in one month. It must be stressed, however, that several problems were which had a serious effect on duction. These have been rectified on the now in operation. 4. The total coal recovery from a pillar is 40 percent. This compares with 70 percent if conventional pillar extraction methods are used. On of the underground a decision was made not to use the auger as an underground mining system based mainly on the low percentage recovery, and into other more methods such as the system. SURFACE OPERATION On 10 June 1988, the auger commenced production on a permanent basis from the highwall of a small contour operation. To date, the auger has been used on both the Gus and Dundas seams. In the contour mining operation the overburden is removed by and dozing the broken material down the of the mountain. In this operation a volumetric ratio of 7: 1 is achieved, resulting in a competent highwall, 7 to 10m high. The highwall is back at an of 15 0, and dressed down to remove loose rubble the operation. Final down of the highwall is carried out hand where dangerous conditions exist. After removing and discarding badly weathered coal from the immediate outcrop area, the coal remaining up to the highwall is loaded front-endloader into trucks for to the beneficiation The coal seams in the area of the contour mining dip gently toward the centre of the mountain, but no problems are experienced the base plate of the machine is resting on the true floor of the coal seam. For this reason, the area below the must be cleared of loose material to pace with the the auger. The auger is fitted with leveuing to position the cutting head, as accurate levelling of the machine reduces the amount of coal which must be left above and below the auger hole. The Gus Seam in the area mined is 700 mm thick and a 600 mm head is used for augering. In the underlying Dundas the bottom coal is 600 mm thick and is mined using a 500 mm diameter cuthead. 412

9 Holes of up to 70 m in are drilled, but many holes are considerably shorter owing to the presence of dolerite dykes which cut the highwall at various An area of burnt coal is found adjacent to the dykes and the auger is as soon as burnt coal is observed from the auger holes. The cutting head sumping rate is good, with a time of 60 seconds per individual auger section, each with a length of 2,0 m. However, it takes 20 minutes to extract an auger with a length of 50 m, which has a serious effect on the overall production rate of the machine. Efforts are now concentrated on the reduction of time spent on non-productive operations, such as withdrawing the auger and moving the machine to the next hole. The machine is trammed using an underground scoop, which is also used for clean-up duties along the highwall. The coal carried out of the holes by the auger flights is conveyed by an armoured flight conveyor onto a conveyor, which the coal in conical ready for loading and transporting to the plant. The auger is operated with a crew of three, plus a scoop driver. 11 shows the machine drilling the Dundas The of the coal produced by the auger is good, with a high percentage of 38 mm + 0,5 mm, which is ideally suited to beneficiation using dense medium cyclones. little crushing is due to the virtual absence of + 38 mm material. After the highwall has been augered, the area will be backfilled to restore the original contours. Full rehabilitation to an approved plan will follow. The cost per sales ton produced by the auger compares very favourably with that of other mining methods employed at Hlobane. Production rates been lower than initially planned. The maximum production rate achieved since 10 June 1988 has been 232m (66 ROM tons) drilled in a shift. The auger has a production rate of I 000 ROM tons per month on a shift, when drilling 500 mm diameter holes. A higher production can be expected for the 600 and 700 mm cutting heads. The production achieved during August 1988 are in Table I. The auger production rate, in metres advance using a 500 mm diameter head, is shown graphically in Figure 12. Availability and utilisation of the machine are given in Figure 13. It can be seen from the graphs that an upward trend in production and utilisation is evident. This upward trend is due to minor problems solved, and also due to the experience gained by and maintenance An additional the auger is that reserves which would otherwise not be mineable by underground methods are being extracted. The workings are only advanced to within 30 to 100 m of the outcrop, as weathering causes the roof conditions to deteriorate. the coal from this weathered zone is the only practicable method of recovering these reserves methods are not economic due to the stripping ratio). Thus, although the auger has a total seam recovery of only 40 percent, the mine is by this percentage of the reserves, which would otherwise have been written off. 413

10 AlA CAPITAL COST OF AUGER The machine described in this paper was designed and built personnel at Hlobane Colliery. This was necessary to the unique parameters required for the auger. The machine has a total cost of R , which can be broken down as follows: Cost in Rand Electric motors (two) Hydraulic pumps (two) 9600 Hydraulic motor Hydraulic Valve bank sections and cutting heads (500 mm, 600 mm and 700 mm) units 4700 Electric switchgear Steel Hydraulic pipes, electric cable and other items TOTAL LABOUR COSTS The total labour cost to construct the auger was R This does not include work carried out by and management group employees. CONCLUSION An auger machine designed to drill circular holes with a diameter of 500 to 700 mm, and with a length of up to 70 m, has been brought into production at Hlobane Colliery. The auger was constructed at a total cost of R , and was and built at Hlobane by Hlobane personnel. Although the auger was designed for both surface and underground the results of the underground trials were not sufficiently encouragto warrant further development. After the underground trials it was decided that the auger would be restricted to surface The cost per sales ton achieved the surface operation compares very favourably with other mining methods employed at Hlobane. The production rate lower than and efforts are being made to improve on the results achieved to date. As the auger has a crew of four, the labour productivity is The surface has the added advantage of the overall recovery of the reserves, thus extending the life of the mine.

11 415 ACKNOWLEDGEMENT Mr B.C. Senior General Mining, Iscor for to publish this paper. LIST OF COMPONENTS INDICATED IN FIGURE 3 1. Hydraulic cylinder to extend and retract anchor jack Hydraulic motor 4. Sliding drive unit 5. Slide rails 6. Multi-stage hydraulic cylinder 7. Levelling jack 8. 37,5 kw motor for equipment 9. Tank for hydraulic oil 10. Power pack kw electric motor 12. pump 13. Position of operator J4. Hydraulic valve bank 15. Auger coupling 16. Base plate 17. scroll 18. Lifting device 19. Armoured conveyor 20. conveyor

12 .j:.. '" TABLE I Production Figures for August AUGER REPORT AUGUST 1988 Metres Time Working Eng Prog Prog Date Metres Prog Available Prog Time Prog Downtime Prog Available Utilizing Met/hr Target Call I I I I I I I I

13 417 DEPTH Om ~ ----, ZUINGUIN DOLERITE SANDSTONE MA TSHONGOlOlO DOLERITE 100m _. SANDSTONE WITH SHALES 200m _. ELAND BONAS FRITZ ALFRED GUS DUNDAS ICOAl SEAMS WITH isandstone PARTINGS COKING 300m SANDSTONE FIGURE I General stratigraphic section at H lobane mine

14 Fine grained Sands tone grading upward ~ to a (oarse grained Sandstone :LAND SEAM O,24m COAL 7,OOm Sandstone ~ONAS SEAM..... O,44m COAL S,OOm Sandstone RITZ SEAM O,SSm COAL 7,OOm Sandstone LFRED SEAM l,60m COAL ,OOm Sandstone and Shale US SEAM O, 98m COAL 9,OOm Sandstone PPER DUNDAS SEAM ~--~ O,40m COAL S,60m Sandstone UNDAS SEAM 1,SOm COAL with Sandstone parting 20,OOm Sandstone Bioturbated OKING SEAM O,25m COAL Fine grained Sandstone 418 FIGURE 2 General section o r coa l sea ms

15 0J-,...,... 'i5\ ' \ NOT[ 11 [ABLE S AND HOSES HAVE BEEN OMITTE O FOR ( LARin' II REF ER TO LIS] ] 0 10EN TiF ) [OMPONE NTS _,1 1" 12 3) THE METHOD Of EXTRA CTING BO TT OM (OAL from DE VEL OPED PIL LARS IN THE DUND AS SEAM IS SHOWN IN THIS FIGU RE..,. 'D ~ FIGURE 3 Components of the auger machine

16 ,, ~.~ n. oj) c ::l u '.~ e,,8.. 7g? W w..j " QO tl:~ 0.. u " oj) c '~ -5l E 2 oj) '" Ci 420

17 FIGURES Cutting head showing pick configuration FIGURE6

18 ... N N Note Guards have been omitted for clarity FIGURE 7 General view of sliding drive unit

19 \ \

20 ... ~ SHALE ,...-;; ~.07m ROOF.. SANDSTONE. " 1 I O.9m.. 1,67m O,7m FLOOR SANDSTONE.: FIGUR E 9 T ypical secti o n o f the Dundas Seam in the a rea o f tile trials at M ountain A dil

21 FIGURE 10 The au ger in opera tion in the underground workings o f M ountain Adit -'=Tr.IIO):;' I'

22 ~ UTILISATION fll%m AVAILABILITY AUGER REPORT AUGUST 1988 METRES "" - ---m -- 1"" "1-- I I I I Iii I III I II II II to It t DATE,III. I I 11 _ M/HOUR bt u!! M/SHIFT FIGURE 12 Auger production rate during August 1988 I ' PERCENTAGE 100, ". :: 40 i: :: r 20 'I ~ ~' ~. ~~ o 1 :' :~.., DATE