Haulage incline top layout
Fig shows an incline top layout where a direct rope haulage and tubs varying from 0.8 to 1.1 m3 capacity with pedestal bearings are used. In a coal mine the layout is capable of handling nearly 600 tubs per day of three coal rising shifts and is typical of the mines having little mechanisation and utilising manual labour for tramming of tubs at the incline top.
The tubs are hoisted in set each consisting of 3 to 6 depending upon gradient of the track and horse power of haulage engine. The loaded set is lowered and fed by gravity along suitably graded track to the side-on-tippler T1 which is situated at a high level on gantry to permit of arrangements of screening plant and passage of railway wagons or trucks below. The empties are pushed manually to the point P, where they are attached in a set to the haulage rope and then lowered into the incline.
If tippler T1 cannot be used due to stoppage of screening plant or non-availability of wagons or trucks, an end-on tippler T1 is used for sipping the mineral into a dumping yard. Dumping space is, however, limited by the height of the tippler and angle of repose of the mineral. A travelling tippler is sometimes used for facility of more .dumping space. Additional space is provided along a branch line L which is utilised by manual emptying of the tubs after side-on-tipping. The dumping space is utilised fully by extending the track on the mineral dumps and supporting the long protruding rails on wooden props.
A track M is provided for materials which have to be supplied to the mine and also to carry to workshop the motors, pumps, etc. which are brought from underground for repairs. It also serves to bring to the main line empty tubs which sometimes roll down the mineral dump when tipping manually.
An inter-connected stop-block and runaway switch SS1 is required at all incline mouths. The distance SS] is nearly equal to a length of a set of tubs plus 4.5 m.
The gradient from the brow to the incline mouth and in the incline is steep, nearly 1 in 5, and from the haulage engine to the brow the gradient is dipping at nearly 1 in 80.
Repairs to tubs are affected on the branch line L, which may be utilised for standage of tubs temporarily out of use.
Inclines or drifts from surface to the mine may also be equipped with endless haulage, balanced direct haulage, belt conveyor or a locomotive as the main transporting medium where high outputs are to be handled. The locomotive, due to the nearly flat gradient required for its operation, finds a limited application.
Conveyor incline top layout
With a belt conveyor, the incline top layout may take the shape as shown in fig. 6.6 for a coal mine. Main belt discharges the output into an overhead bunker from which coal is tapped into the railway wagons or trucks. Alternatively, a small cross belt may take the coal from the main belt to a ground bunker, which is easier and cheaper to construct and which can augment its capacity by allowing an almost unlimited ground stock to be spread over and about it. The ground stocks can subsequently be pushed into the bunker by dozers. At the bottom of the ground bunker are chutes which discharge coal on to a high-speed belt delivering into railway wagons or trucks through another chute. This arrangement will allow the raising of the mine to continue uninterrupted throughout the day and enable wagons to be loaded when supplied, within the free time allowed by the railways.
When access to the deposit is by a deep shaft, the raising pit may be fitted with a cage winding installation or, a skip winding installation.
Pit—top layouts for cage winding pits
In the case of pits the winding of men and material is by cages, or by skips. Winding by single deck cages, either a single cage or a tandem cage, is the common practice in this country. Multiple deck cages are common in foreign countries and are also employed at modern mechanised mines like Sudamdih, Jaduguda and others. For deeper shafts skips are preferred.
The term "tub" is in common use in the colfields and the term "mine car" normally is used for tubs of 1.25 te and higher capacity, with or without brakes, it is a standard practice to have roller or ball bearings for the wheels of a mine car.
The raising capacity of a mine depends on the shaft capacity which in turn, depends on the manner in which tubs or mine cars are handled at the pit-top and pit bottom. The design of pit-top and pit bottom layout is done with the following objects in view.
(1) Use of the shaft to its full capacity.
(2) Use of minimum number of tubs in the circuit.
(3) Use of minimum number of operatives.
(4) Maintaining steady flow.of tubs.
(5) Minimum decking time.
(6) Lowering of materials.
(7) Handling of ores or coals of different grades.
In any pit top arrangement it is essential that the loaded tub or mine car, raised from the pit, discharges mineral close to the shaft and returns to the cage, so as to require the least number of tubs in circuit. It is also imperative that mine cars are not allowed to run freely under gravity over long distances.
Run round arrangement
A run-round arrangement is shown in Fig 6.7. From the decking level, the loaded tubs are taken to the tippler T via weighbridge W and empties travel by gravity to a creeper (which elevates them to a little above the decking level) and gravitate to the other side of the cage. A creeper on a load side is not desirable and the usual arrangement therefore is to have the decking level 4 to 6 m above the ground level on gantry. A weigh—bridge for all the mine cars raised from the pit is a good practice but is uncommon in our mines. If the quality of mineral raised from the pit is not uniform, sometimes due to working of two or more seams of coal (or ore from 2 different levels) by the same pit, two or more tipplers have to be provided for the different grades. The figure shows coal of two* grades coming from the different seams, each raised by a separate pit. One tippler T1 has been provided for the loaded tubs containing shale or stone, which may be disposed of by a belt conveyor. Provision may be made for alternative arrangement to unload the coal tubs, when the usual tipplers cannot be used due to breakdown or stoppage of screening plant. Such arrangement consists in providing one or two travelling tipplers, depending upon the output for tipping the coal into a dumping yard.
When the decking level is above the ground level, the materials are lowered into the mine by loading them into the cage at ground level and an opening in the shaft walling, equipped with a gate and a track, is provided for this purpose; alternatively, a hoist is used for taking materials to decking level.
The main disadvantage of a run-round arrangement is the large space required and the long circuit which the tubs have to pass, specially with long wheel-base mine cars which require large radius curves. (For other pit top layouts see Vol. III of this book).
Pit-bottom layouts for cage winding
The type of pit bottom layout to be followed depends upon the type of transport system used in the vicinity of the pit bottom and the method of winding, whether skip winding or cage winding. The pit bottom layout lasts the whole life of the pit, and has to be designed to meet the maximum production likely to be handled by the pit, as rearrangement of pit bottom is expensive and may involve costly excavations in stone over a wide area, resulting thereby in weakening of the shaft pillar. The rearrangement takes a long time and hampers normal production.
Though a pit bottom layout essentially depicts the transport arrangements near the pit bottom to deal with a targeted output, ventilation, drainage and support arrangements have to be considered in designing it.
Rope haulage layout.
A common layout, typical of many Indian coal mines, using rope haulages and cage winding, is shown in Fig. 6.8, considering ventilation by exhaust fan, which is the normal practice. The points to note in the layout are:
1. Winding of coal is from only one level which is in the coal seam so that pit bottom decking arrangement is in coal.
2. Shaft on the dip side is D.C, and the main coal winding shaft.
3. The two shafts are connected by a roadway provided with an air-lock and a track for materials. Materials are generally lowered from the surface by the U.C. shaft which has little output, if any, to handle. The air lock consists of three doors, two opening towards the D.C. shaft against air pressure. The third door, opening in opposite direction, is required in an emergency which may necessitate reversal of ventilation system. Distance between the two doors should be not less than the longest timber or rail likely to be transported through the air lock.
4. D.C. shaft carries high voltage cable from surface to the sub station near the pit bottom. U.C. shaft being warmer is generally not preferred for power cables. D.C. shaft carries telephone cables also.
5. Main delivery column from pit-bottom pump is taken to surface by the D.C. or the U.C. shaft according to convenience.
6. A by-pass is provided near the pit-bottom for persons to go from one side of the pit bottom to another without crossing the pit.
7. The shaft levels in East and West directions are not exactly level, but slightly dipping towards shaft-bottom at a gradient of I in 80 to 1 in 120, depending upon the type of tubs or mine cars used. This facilitates drainage also.
8. The shaft levels are equipped with double tracks, one for empties and the other for loads, on either side of the shaft. A stop block on each track near the cage is essential and diamond crossings are provided to give clear space of only 2 to 4 tubs near the cage. Tub retarders are also used in the shaft level near the pit bottom. Ordinary tubs, with 1.1 m1 capacity, can often be slowed or even stopped by the use of sprags and may obviate the need for retarders.
9. A third track or siding 10 to 15 m long has to be provided for standage of material transporting trolleys.
10. Standage for loads has to be provided on East and West shaft levels for occasional stoppages of winding system. The standage generally provides for half an hour's output during peak raising periods. Considering a raising of 30,000 te per month or nearly 1200 te per day with three working shifts or 400 te per shift, and assuming that this is raised in six hours of an eight-hour shift, half an hour's output is nearly 35 tubs, each of one te capacity. Shaft level on either side of the pit should have standage for about 20 tubs i.e., clear space of nearly.40 m.
11. The endless haulages are situated near the shaft bottom. The dip districts are served by direct haulages and the rise districts by tail rope haulages. Crossing of direct and endless ropes is avoided by either of the arrangements shown at A1 and A. At A1 the endless rope passes above the direct rope. This reduces the span of the bridge which has the further advantage of supporting only slow moving traffic of endless haulage. At A2 the loads are taken over a brick ramp which is raised in the middle for movement of loads, when detached, by gravity to the shaft level. For empties, the track is suitably graded from the shaft level to the clipping point at A2 for supply to the dip district.
12. 12. The shaft pillar occupies an area KLMN in which only essential excavations and galleries are made for haulage, drainage, ventilation, etc. These include a main sump with overflow gallery T1, main underground sub-station S1, fire fighting station F, an underground office S, an underground store and ambulance room V. The office, stores and ambulance rooms should be away from tub traffic; for high output which involves heavy mechanisation an underground workshop is desirable.
This type of layout will serve upto 30,000 te/month and the haulage arrangements will work on gradients from 1 in 4 upto 1 in 12. For gradients milder than 1 in 12, endless haulage should replace direct haulage.
Underground crusher level layout in a metalliferous mine is shown in Fig. 6.11. The figure shows the layout between level 7 and 8 at Mochia Main Mines, Zawar (Hindusthan Zinc Limited) in Rajasthan. The shaft is equipped with tower mounted koepe winder for skip (400 H.P.) and another tower mounted koepe winder for cage (200 H.P.) The cross-section of the shaft, rectangular in section, is 5.2 m x 3.8 m. It has a capacity to handle 1200 te of ore per shift of 8 hours. The layout includes an underground crusher and orebin which is a feature of some metalliferous mines but rare in coal mines. The pump chamber and sump are located at 7th level.
Midset landing arrangement.
When mineral has to be raised from two or more seams or 2 levels by the same pit, the arrangement that has to be made in the middle or intermediate seam is known as shaft midset landing arrangement. Where guide ropes are used there are oscillations of the cage during winding and it is not desirable to install fixed receivers at the midset landing to receive the cage. A fixed platform at the midset landing is also not desirable as the cage, because of its oscillations, may strike it. Rigid guides of rail or wood are quite convenient for the cage if midset landing is provided.
The arrangement at midset landing with rope guides is shown in Fig. 6.12 and the main requirements are as follows:
(1) Hinged platforms are used. These are operated by levers, manually handled. The two platforms on either side of the shaft at midset are interconnected by rods and links. The platforms bridge the space between the midset and the cage at each side of the shaft. When the platform is lowered it is supported by buntons fixed well clear of the cages and comes in level with the floor of the cage. Counterbalancing weights are used to manipulate the platform.
(2) Safety gates are provided at each side of the midset landing. These are of the sliding type or collapsible type. They may be so interlocked with the lever or the hinged platforms that unless the platform is lowered in position, the gates cannot be opened.
(3) Stop blocks are essential to control tubs at the midset.
Telephones and arrangement for coded signalling to pit top are required. A separate and distinct code of shaft signals should be used specially for the midset landing only. It is desirable to have red and green light signals which will automatically operate with the manipulation of hand lever of hinged platform. The pit top banks man can then know whether the midset is free for cage winding (green light on) or whether some work is going on at midset (red light on).
When two seams or two levels are being worked by the same shaft and both have practically the same output, it is convenient to make such arrangements of winding that when one cage is at midset the other is at pit bottom decking level. This can be arranged by use of differential drums, i.e. two drums of different diameters on the same shaft of winding engine. Fixed platforms can then be used at midset.
Drainage of shaft bottoms and the main sump
If a shaft carries guide ropes, these are loaded with cheese weights at the bottom end to keep the guide ropes taut, permitting only little oscillations. Shafts are, therefore, sunk 4.5 m to 6 m deeper than the pit-bottom decking level to accommodate the cheese weights. To avoid water of the pit bottom over-flowing into the shaft level and also to keep the cheese weights clear of water, provision has to be made for drainage of the shaft bottom. The arrangement may employ one of the following methods.
(1) One pump is installed in the shaft level and suction pipe is placed in the shaft bottom below the decking level. The pump is worked as and when necessary to pump out water accumulation below the decking level. A ladder from the decking floor to the pit bottom gives access to the foot valve and strainer of the suction pipe. This method is applicable where pit bottom is only 3 m to 5 m below the decking level and guide ropes are preferably clamped to avoid, congestion by guide ropes, cheese weights and pump-suction below the decking level.
(2) Water is allowed to gravitate to the main sump by connecting the pit bottoms of both shafts to the sump by a drift dipping towards the sump. Fig. 6.13 shows the D.C. and U.C. shafts connected at the bottom end by a level gallery in stone. To prevent short circuit of intake air to U.C. through the connection, a constant water seal is maintained by the proper design of the gallery as shown in the figure and the muck is cleared by an auxiliary winch and bucket at intervals.
A staple pit with a ladder, or a stone drift from the coal seam, gives access to the drainage drift. This arrangement is commonly adopted.
(3) Submersible bore hole pumps may be used in the bottom. The submersible bore hole pump has its bottom at least 400 mm clear from the pit bottom. The pump can be raised or lowered by a winch placed in a roadway driven in stone below decking level. The roadway has access from the shaft level by a staple pit or by a small drift. Three electrodes are suspended from the shaft and reconnected to an electrical system. The continuity of electrical circuit is through the water in the pit bottom; if the water level falls below the middle electrode, the continuity is broken and a relay trips the current to the motor. The pump is self priming and is arranged to start and stop automatically. Access from winch gallery to the pump is by a ladder.
Main sump
Water from all the districts of -a mine is collected at a main sump situated on the dip side of the pit bottom, the usual arrangement in a coal mine being as shown in Fig. 6.15. The galleries are driven through coal to store the water. The essential features of the main sump are:
1) The dip most "level" galleries should dip towards the junction to facilitate water flow towards a common point. The junction is the suitable place for strainer and foot valve. To keep the latter always under water, it is helpful in flat seams to make a small pit, say 1.8 m dia x 1.2 m deep, at the junction.
2) The suction head including friction should not exceed 6 m for smooth and trouble-free operation of the pump; if necessary, level galleries of the sump may be at shorter distance than that prescribed in the Regulations with prior permission from the D.G.M.S.
3) The sump should be able to store water for 24 hours during rains in case of pump failure. More storage capacity will require more number of galleries in the main sump.
4) An overflow arrangement should be provided. The overflow gallery should be connected to a dip gallery which should not have a haulage track, otherwise the overflow will wash away the tram line packing. Where this is not practicable the dip haulage gallery should have a drain for overflow water.
5) The pump house should have standby motor-pump unit and it should be so situated that it is not affected by overflow water of sump. It should be well ventilated by intake air.-Track should be laid from shaft to pump house for transport of pumps, motors, pipes, etc. and extended upto foot valve when the sump is to be cleaned by loading muck on tipping tubs. The pump house should be spacious to accommodate pumps, motors and switchgear. It should be high enough to permit provision of lifting tackles over the pump and motor.
Main sump with two wells.
Another type of main sump with double sump arrangement is preferred in a mine where sand stowing is practised. Water from sand stowing districts invariably carries sand which is pumped to the main sump by the in bye district pumps. The main pumps therefore wear fast and need frequent repairs and overhauls when pumping gritty water mixed with abrasive sand. It therefore becomes necessary to
(1) Clean the main sump at intervals,
(2) provide additional sump when one sump is being cleaned,
(3) Arrange water from the district pumps to pass through a settling tank or similar arrangement where sand can settle down.
One such arrangement is shown in Fig. 6.15. The pump house is common for both the sumps. Each sump has its galleries so arranged that the water gravitates to the well which carries the suction pipe, foot valve and strainer of the pump. The well may be nearly 6 m deep and 1.5 m dia. The two wells are connected 0.6 m below the top by a 200 mm dia pipe fitted with a sluice valve so that the water may be shared by both the wells when one of the wells is nearly filled to the brim. Excessive overflow water is stored in the drift and the levels which form the sump. Each well is provided with arrangement for lifting the suction pipes.
By arranging discharge of the district pumps to feed only one sump and the well serving it, suitable arrangements can be made to keep the other sump and well out of use and free for cleaning.
Chinakuri colliery is provided with arrangement of double sump
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