GB2093123A - Hydraulic conveyance of debris - Google Patents

Abstract

In a system for the pressurized water conveyance of the debris from underground mining, two overlapping face conveyors are provided, one conveyor 1 advancing with the working while the other conveyor 2 is moved up stepwise at extended intervals to maintain overlap with the first conveyor. The conveyor 2 is connected with, and delivers into a transfer tank 7 which is connected to the discharge line 10 and the water supply line 9. A slurry pump 14 is disposed in the discharge line between the tank 7 and the valve 15. The discharge line 10 and supply line 9 are composed of readily connectable sections and shut-off valves are connected at intervals in the lines 9, 10. When the second conveyor and tank 7 are to be advanced, first the nearest shut-off element is closed and the water in the supply line 9 downstream of that element is pumped into the discharge line section 10, after which the nearest shut-off element in discharge line 10 is closed and the water in line 10 upstream of the shut off element is returned to the tank 7 via bypass 17, after which the tank 7 and adjoining line sections 9b, 10b are separated from the lines 9, 10, the tank advanced. <IMAGE>

Description

SPECIFICATION System for the hydraulic conveyance of debris in underground mining and method of operating the system This invention relates to a system for the hydraulic conveyance of debris yielded in underground mining, such as coal mining, in operation of which system said debris is conveyed along a conveying pipe by pressurized water. Such a system may be utilized in longwall working using stripping and/or cutting.In particular, the invention relates to such a system comprising at least one face conveyor which moves together with the advance of the face and which, in use, is situated in the gate and which serves to take over and convey onwards the debris yielded at the face and, where applicable, in tunnelling, the system also comprising: a buffer bunker between the working area and the conveying pipe for temporary storage of the debris; a crusher for reducing the debris; and a pipe loop which has a pump unit and shutoff elements and which includes a transfer tank which follows the face conveyor, is entrainably connected thereto and serves to introduce the debris into the conveying line, the intake and discharge lines of the loop being adapted to be short-circuited by means of a closable by-pass line with exclusion of the transfer tank.The invention also relates to a method of operating such a system.

German Offenlegungsschrift 28 20 020 discloses a system and method of this kind for the hydraulic conveyance of the debris evolved in mining operations.

The advantage of hydraulic conveyance systems over the conventional "dry" conveyance of such debris is that they do not represent a dust or fire risk in the mining zones behind the working and they reduce the risk of accidents due to the virtual absence of rotating machinery.

Furthermore, hydraulic conveyance systems do not have the disadvantage of heating the mine atmosphere. The flow and return sections of the conveying line take up less space in the levels than conventional conveyors. The increased space which results, more particularly in the gates, can be used for the trackless technique, which enlarges the system. Hydraulic conveyance is much more tolerant of curves and gradients than other conveyors, needs considerably less attention and maintenance and reduces stoppages and interruptions by virtue of its greater reliability than conventional conveyors. Yet another advantage is that hydraulic conveyors are more adaptable in their capacity and additional hydraulic pit conveyance is a relatively simple way of increasing existing pit capacity which may have become too small.Another advantage is that hydraulic conveyance in one section can readily and simply be combined with existing conventional main road or pit conveyance; also hydraulic conveyance systems are more readily applicable to a variety of Situations, because they are simpler to assemble and dismantle than other forms of conveyance system.

Hydraulic conveyance systems of the kind to which this invention relates have substantial advantages over the known system of hydraulic conveyance with "open" channelling of the water, in association with hydromechanical winning, and concentration of operations makes it possible to provide a much increased and therefore more profitable, conveyance at the point of operations, without difficulties due to storage problems.

Consequently, in contrast to the circumstances associated with hydraulic conveyance using "open" water conveyance, strike, rise or dip facing working can be used for advance working and for retreating working irrespective of whether and to what extent the working or face extend over saddles and troughs.

More particularly, in addition to greatly improving workplace ergonomics underground and to reducing running costs substantially, conveying processes of the general kind to which the invention relates, and the associated conveying systems make possible further rationalisation of support services and, therefore, simplification and improvement of operations, improved accessibility of workpoints resulting from compact equipment and greater mobility of manpower and equipment.

Capacity can also be increased considerably in existing plants, for instance, by the provision of continuous conveyance all round the clock.

The earlier suggestion relating to the system or process of interest in the present context is that the debris yielded in the face and possibly in tunnelling should be transferred to a face conveyor situated in the gate, crushed and supplied to a gate bunker which also serves to introduce the debris into the line loop. It was proposed also that the face conveyor, the crusher associated therewith and the gate bunker should be changed over or advanced or moved back by appropriate adaptation of the length of the flow and return sections of the conveying line in accordance with the advancing face exit following the same as closely as possible.The changeover in the roadway direction can be continuous, for instance, with the use of hydraulic cylinders, or stepwise, but in all cases in such manner that the mobile unit comprising the short conveyor, associated crusher and gate bunker move up in the face as the working advances.

Also, in accordance with the known proposal, the hydraulic flows from all or some of the working stations flow by way of a pipe grid to a central bunker which is near the shaft, whence in known manner the product is pumped through risers in the shaft up to the surface preparation facility and dewatered there to recover the return water. If, however, only some working points have hydraulic conveyance facilities, it is recommended in the known suggestion that the hydraulic flows should be combined in a central bunker and that dewatering should be carried out underground.

Advantageously in this case, the solids content of the mixture is broken down in a fine fraction and a coarse fraction, only the fine fraction being pumped as slurry, through the agency of known feeders and risers in the shaft, to the surface preparation plant, whereas the coarse fraction, possibly after intermediate bunkering and an admixture of "dry" and conventionally conveyed debris from other working points, is either conveyed to the surface by means of conventional shaft tubs or re-used as stowage material as required underground.

In a system in accordance with the known proposal, considerable difficulties are encountered in rational lengthening of the flow and return sections of the conveying lines to follow up the stepwise advance, in accordance with the rate of working of the mobile unit consisting of the face conveyor, associated crusher and transfer bunker serving to introduce the debris into the conveying line. These difficulties arise for a variety of reasons and since these difficulties are to some extent contradictory, they cannot readily be obviated satisfactorily.

Difficulties reside in the first place in achieving, in practice the ideal arrangement in which the necessary lengthening of the hydraulic line sections as the mobile unit advances coincides with down times which occur at the respective workings due to operating conditions independent of the conveying system, so that it is not necessary to stop working at the face simply to advance the mobile unit and lengthen the hydraulic line sections. From the profitability aspect, it would be desirable if the mobile unit could be advanced as the working advances and if the sections of the conveying line could be lengthened simultaneously daily or at intervals of several days, possibly weekly, in the shifts on which operations are in any case based.

Clearly, a very long, possibly weekly, advancing and lengthening cycle is preferable on the grounds of profitability if for no other reason than that much of the labour spent on advancing the mobile unit and more particularly lengthening the sections of the conveying line is independent of the length which have to be added to catch up with the rate of advance of the workings, and so it would be more economical to advance the mobile unit and lengthen the conveying line only at very long intervals of time.

A first difficulty arising in this connection with the known system in that, because of space restrictions in the road or gallery, the transfer bunker combined with the relatively short face conveyor to form the mobile unit can have only a limited storage capacity because of the restricted cross-sections in the roadway and usually this is only just sufficient to even out the natural irregularity of the conveyed flows from the face and tunnelling in order to ensure very uniform hydraulic conveyance away from the workings.

Also, the pipe or line sections used for the conveying line have an inside diameter of between approximately 200 and 250 mm and for obvious practical reasons can have only a standard and relatively short length - as a rule, approximately 5 hand the resulting unit of length or a multiple thereof can be harmonized only with great difficulty or, even more likely, by change in very favourable circumstances, with the daily rate of advance at the workings.

The resulting unavoidable need to stock a large number of adapters graded in length to one another is not only a nuisance but calls for correspondingly more labour for lengthening the conveying line sections as the working advances.

Also, when the conveying line sections are being lengthened, care must be taken to ensure that there are no substantial losses of conveying water or slurry from the disconnected line sections which may accidentally reach the roadway.

One way of inhibiting the discharge of large quantities of water or slurry would be to provide shut-off elements in the form of valves or the like at appropriately short intervals along the flow'and return sections, e.g. between every two consecutive sections. However, this idea is far too costly, irrespective of whether the shut-off elements are left in the line at relatively short intervals or are replaced or changed over occasionally when a lengthening operation becomes necessary.

In the known system of the kind of interest in the present contact the only other possibility is first to pump into the transfer tank or bunker, by means of the pump unit in the flow section of the line, the conveying water present in the section immediately upstream of the tank or bunker and extending as far as the next shut-off element, but this would be impossible for the return section of line since the bucket-wheel lock cannot operate as a pump. Quite apart from this, both alternatives become impossible when the combined transfer tank and bunker already contain an excessive amount of debris and/or the quantity of water or slurry to be pumped back into such tank exceeds the storage volume still available due to the shutoff elements in the line section being too far apart from one another.

In order to make full use of the advantages of the known system while obviating its disadvantages it is the object of this invention to enable the transfer tank to be advanced, and the sections of conveying line to be lengthened in association with the advance, at longer intervals and more rationally than has previously been possible, without the risk of large quantities of conveyed water or slurry entering the roadway while the extension operations are proceeding.

The escape of large quantities of water or slurry into the roadway may have the long term effects, familiar to the miner, if the surrounding rock is sensitive to water, of damage to the road crosssection and more particularly the support system.

To solve this problem, the invention proceeds from the known system but departs therefrom in that the system comprises two face converyors which are adapted to overlap over most of their length and are movable relatively to one another lengthwise, the first conveyor, which has the crusher and serves to bunker the debris, moving the advance of the working either continuously or stepwise at short intervals, while the second conveyor, which is entrainably connected to the transfer tank, can be moved up in accordance with the length of overlap only at relatively long intervals which are adapted to the daily rate of advance or to an integral multiple thereof, preferably to the weekly rate of advance; and the transfer tank, which serves as a mixing tank to form the slurry from at least substantially the conveying water and the debris, is connected at its end remote from the conveyor and near the ground to the discharge line of the line loop, to which line the slurry pump and a shut-off element are connected before the bypass line, while another shut-off element is connected in the supply line of the pipe loop in the section between the mixing tank and the bypass line, and the line sections bounding the same, including the shut-off elements installed in such sections and the slurry pump, form -- during the separation and lengthening of all or parts the conveying line, which is subdivided into sections and which is adapted to be closed over relatively long lengths by shut-off elements -- components, rigidly connected to the mixing tank, of that part of the system which is adapted to be advanced at longer intervals jointly as a unit in relation to the bunker conveyor.

This arrangement makes it possible not only to advance the mobile unit comprising the transfer and mixing tank, and to carry out the associated lengthening of the line sections economically and at long intervals and substantially independently of the rate of operations at the workings but also to ensure that there is little loss of conveying water or slurry to the roadway when the line sections are lengthened, although the shut-off elements which must be provided in the line sections can be provided at substantially increased intervals of preferably e.g. 100 m.

Since the mixing tank no longer has to double as a bunker for the debris, substantially its entire storage capacity can be used, before lengthening of the line sections, to receive the volume of liquid present in the upstream line sections as far as the next shut-off element, without having to be excessively large for this reason. If the line sections have an inside diameter of 250 mm and the shut-off elements therein are provided at intervals of 100 metres, the consequent volume of the mixing tank is only 5 m3 - i.e. an order of magnitude which can readily be provided without appreciable reduction of the roadway crosssection.

By virtue of the special by-pass facility and associated slurry pump in the system according to the invention, the mixing tank need to receive additionally only the volume of liquid in one of the two line sections and not necessarily the volume of liquid of both such sections.

According to another aspect of the invention there is provided a method of advancing the unit of a system according to the invention which follows the working in which method, before the unit advances, first the nearest stationary shut-off element in the supply line portions to the rear is closed, the conveying water trapped in the line portion between the mixing tank and the closure zone discharges into the mixing tank and the corresponding volume is forced, if necessary by means of the slurry pump, into the discharge line section, whereafter the nearest shut-off element of the discharge line portion to the rear is closed and the content present between the closure zone and the mixing tank discharges thereinto, possibly with the assistance of the bypass line and avoiding the slurry pump, whereafter the emptied portions of the supply and discharge sections of the conveying line are separated and the mixing tank together with the second face conveyor and the line portions remaining connected thereto are advanced in accordance with the rate of working, whereafter the interrupted conveying lines are reconnected by means of additional pipe sections, possibly in the form of adapters, and of the telescopic tubes.

Conveniently, the two overlapping and relatively mobile movable face conveyors are in known manner chain scraper conveyors; the extent of overlap depending, in dependence upon the rate of advance of the workings, on whether the mobile unit is advanced, and the flow and return sections of the line lengthened, daily or at intervals of several days or just weekly. For instance, for a daily rate of advance of 5 mm the overlap would have to be at least 5 m, whereas if the advancing and lengthening procedure is carried out weekly, the overlap would have to at least be 25 m.

The bunker conveyor which has the crusher and which, conveniently, overlaps the second face conveyor, has in accordance with a preferred feature of the invention a length which is increased to correspond to the required storage capacity and, where applicable, a correspondingly larger conveyor cross-section than the second face conveyor, control or adaptation of its storage capacity being effected by appropriate control of the rate of conveyance.

The bunker conveyor having the crusher has, in the region overlapping the second face conveyor entrainable with the mixing tank, at least before the crusher and on the ground, a screen for direct transfer of the fine-grain proportion of the debris to the following conveyor, without the fine grain having to pass through the crusher. Of course, further screening can be provided in known manner after the crusher and the oversize grain yielded in this zone can, if required, be returned to the crusher. For the rest, the size of the particles supplied to the conveying line depends upon circumstances, more particularly the inside width of the conveying line and, where applicable, whether additives, such as bentonite, are supplied to the mixing tank to improve the suspendability of the slurry and thus facilitate hydraulic conveyance.

Preferably, the grain size is less than 100 m and possibly only 60 m.

To obviate unwanted blocking of the debris in the mixing tank, the base thereof, is conveniently, inclined towards the orifice of the return line section, the feed section of the line loop extending into the mixing tank at the end remote from the face conveyor whereas the return line section is connected at the correspondingly lower level to the opposite end of the mixing tank.

Preferably, the slurry pump is a sludge pump; however, other facilities known to be suitable, such as pipe feeders, pressure vessel conveyors or the like can be used for this purpose.

Advantageously, to avoid as far as possible the use of adapters in the step of lengthening the sections of line, the end portions of the supply and discharge line sections of the line loop which extend beyond the bypass line are telescopic tubes which are also part of the unit which follows up the working at relatively long intervals.

Preferably, the system is for the rest so devised that the content of that portion of the supply line section which is shut off before the by-pass line as considered in the flow direction can be forced by the slurry pump by way of the mixing tank into the discharge line section of the line loop; and the content of that portion of the discharge line section which is shut off after the by-pass line as considered in the flow direction can be discharged into the mixing tank by way of the by-pass line avoiding the slurry pump. This feature is in any case preferable whenever it is inadvisable -- or the slurry pump is not adapted -to deliver at least temporarily against the flow direction.

A convenient embodiment of the invention will be described in detail hereinafter with reference to the drawings wherein: FIGURE 1 is a diagrammatic view of a system, embodying the invention, in side elevation; FIGURE 2 is a view to an enlarged scale and in perspective of the part A of Figure 1, and FIGURES 3, 4 and 5 are diagrammatic views of three consecutive working steps in the advance of the mixing tank and the lengthening of the sections of the conveying line.

Referring to Figure 1 , there can be seen a bunker conveyor 1, which follows the working either continuously or stepwise at short intervals, and a second face conveyor 2, which overlaps the conveyor 1 and follows the working at longer intervals than does the conveyor 1. Both the conveyors 1, 2 are chain scraper conveyors as are basically familiar in underground mining; consequently, no further details need be given of their construction.

Debris is transferred from the face (not shown) at a place Y of the bunker conveyor 1. Any debris arising in tunnelling can also be transferred at place 1, although the tunnelling is not shown either.

The bunker conveyor 1 comprises in a known manner a crusher 3 which can be of any known kind.

Referring to Figure 1, a screen 4 can be placed on the floor of conveyor 1 in the region before the crusher 3 and enables the arriving debris, to the extent that it is of a grain size passing the screen, to be transferred before the crusher 3 to the second conveyor 2 therebelow.

For the rest, the crushed debris is transferred to the second conveyor 2 at reversal station 5 of conveyor 1.

The two conveyors 1, 2 overlap by an extent X at least such as to correspond to the daily advance of the working or to a multiple thereof, preferably to the weekly advance. It is assumed in the embodiment shown that the daily advance is 5 m and the conveyor 2 needs to be advanced only once a week. Consequently, the overlap X is at least 25 m in this case.

For the rest, the bunker conveyor 1 is of a length and, possibly, of a conveying cross-section such as to provide, in association with a correspondingly reduced conveying speed, an adequate emergency storage capacity for the arriving debris. It also serves as a buffer between the winning operations and the removal of thwa debris by hydraulic conveyance. The conveyor 1 enables quantities of debris which arise from the face or from heading and which vary considerably per unit of time to be so evened out that a substantially constant quantity of debris per unit of time can be introduced into the conveying line in the manner desirable for satisfactory hydraulic conveyance.

At its transfer end 6 the second conveyor 6 is rigidly connected to a mixing tank 7 through which the debris goes to enter the discharge section of the conveying loop.

As can be seen more clearly in Figure 2, tank 7 has an inclined base 7a facilitating the passage of the debris to orifice 8 of the discharge line section of the conveying loop.

Referring to Figure 2, there can be seen a flow line section - i.e. a section conveying water under pressure - 9 and a return section 10 -- i.e.

a section which removes the slurry. The mixing tank 7 is so incorporated in the loop embodied by the sections 9, 10 that the flow line 9 is connected to the mixing-tank end facing the face conveyor 2 at a height which takes account of the inclination of base 7a.

By means of a shut-off valve 11 in line portion 9a, the inflow of pressure water into tank 7 can be shut off or, if necessary, restricted. The variable length telescopic tube 12 has a cylindrical portion 1 2a which is fixidly and sealingly connected to end portion 9b of flow line section 9.

The telescopic tube part 1 2b is disposed in a cylinder 1 2a; it serves for the connection of the next section of the feed line of the conveying line and facilitates stepless equalisation of any length differences.

A corresponding telescopic pipe or tube 13, 1 3a, 1 3b is used for the end portion of the terminal part 10a, of the return line 10.

Another portion 1 Ob of the return line connects portion 1 Oa to a sludge pump 14 which is in turn connected by line portion 1 Oc to exit orifice 8 of mixing tank 7.

Pump 14 is driven by a motor 1 4a.

Another shut-off valve 1 5 is provided in line portion 1 or.

The flow section 9 and return section 10 can be short circuited in the region between the telescopic pipes 12 and 13, on the one hand, and the mixing tanks 7, on the other hand, by a by pass 1 6 which can be closed or just restricted by means of another shut-off valve 1 7.

As can also be gathered from Figure 1, the tank 7, pump 14, 1 4a and the two telescopic tubes 12, 13 are mounted on separate base plates 18, 19, 20 which are interconnected so as to be articulated vertically and connected to one another so as to be resistant to tension.

Since the second face conveyor 2 is rigidly connected to the mixing tank 7, the conveyor 2, tank 7 and line loop 9, 10 including the pump 14 and the telescopic tube 12, 13 form a common mobile unit which, unlike the bunker conveyor 1, is advanced only at relatively long intervals of time - once a week in the case of the present embodiment -- in accordance with the advance of working in the meantime.

As can be gathered from the diagrammatic views of Figures 3 to 5, the pipe sections are lengthened during or before the advance of the tank 7 as follows: Before the unit or tank 7 is advanced, the shutoff element 24 in the flow line section 9 immediately to the rear is closed and the conveying water trapped in the line section between the tank 7 and the place of closure is emptied into the tank 7; this amount can, if required, be pumped into return line 10 by pump 14, 14a.

The rearmost shut-off element 23 of the return line section 10 is then closed and the line contents present between the place of closure and the tank 7 is emptied thereinto. The pump 14 can be bypassed by means of the by-pass facility 1 5-1 7 through which the content of the line portion between the shut-off element 23 and the mixing tank 7 can flow, after closure of the valve 1 5 and opening of the valve line 1 7 in the bypass 16, through the latter and the flow line section 9a, after opening of the valve 11, into the mixing tank 7, the pump 14, 1 4a being switched off.

The state then reached is shown in Figure 3.

Figure 4 shows by way of contrast the state after the emptied line portions of the flow and return sections of the conveying line have been separated and the mixing tank 7 together with the second face conveyor 2 and the line portions remaining connected thereto, including the two telescopic tubes 12, 13 has been advanced in accordance with the advance of the working in the meantime.

Also, in the state shown in Figure 4, the extension sections 21a, 22a have already been connected to the existing sections 21, 22 respectively.

Figure 5 shows the final state in which, after the unit has advanced and the lines have been lengthened, the interrupted lines have been reconnected by means of the extension sections 21 a, 22a and of the two telescopic tubes 12, 1 3.

Even through the invention greatly reduces the need to use adapters, it may be advisable to keep some available, more particularly if the tube sections are of the conventional length of 5 m. The adapters can in this case be of a length corresponding to one-half or one-quarter of a line section. Preferably, the extent of adjustment of the telescopic tubes is in this case 25% of normal pipe section length.

Claims (16)

1. A system for the pressurized water conveyance in a conveying pipe of debris from underground mining, more particularly coal mining, in longwall working using stripping and/or cutting, the system comprising at least one face conveyor which moves together with the advance of the face and which is situated in the gate and which serves to receive and convey onwards the debris yielded in the face and, where applicable, in tunnelling, the system also comprising: a buffer bunker between the working area and the conveying pipe for temporary storage of the debris; a crusher for reducing the same; and a pipe loop which has a pump unit and shut-off elements and which includes a transfer tank which follows the face conveyor, is entrainably connected thereto and serves to introduce the debris into the conveying line, the intake and discharge lines of the loop being adapted to be short-circuited by means of a closable by-pass line with exclusion of the transfer tank, the system comprising two face conveyors which are adapted to overlap over most of their length and are movable relatively to one another lengthwise, the first conveyor being provided with said crusher and serving to bunker the debris, being movable with the advance of the working either continuously or stepwise at short intervals, while the second conveyor, which is entrainably connected to the transfer tank, can be moved up in accordance with the length of overlap at longer intervals; and the transfer tank, which serves as a mixing tank to form a slurry incorporating the conveying water and the debris, being connected at its end remote from the conveyor and near the ground to the discharge line of the line loop, to which line a slurry pump, constituting said pump unit, and a shut-off element are connected before the by-pass line, which another shut-off element is connected in the supply line of the pipe loop in the section between the mixing tank and the by-pass line and wherein the conveying line is subdivided into sections and is adapted to be closed over relatively long lengths by shut-off elements and wherein the by-pass line and the line sections bounding the same, including the shut-off elements installed in such sections and the slurry pump, form -- during the separation and lengthening of all or parts of the conveying line, components of that part of the system which is adapted to be advanced at longer intervals jointly as a unit in relation to the bunker conveyor, the last-noted components being rigidly connected to the mixing tank.

2. A system according to claim 1, in which the two overlapping and relatively movable face conveyors are chain scraper conveyors.

3. A system according to claim 1 or 2, in which the bunker conveyor which has the crusher has a conveying cross-section which is larger than that of the second face conveyor and/or a relatively long length corresponding to the required storage capacity and is designed for control or adaptation of its storage capacity to suit aiterations in conveying speed.

4. A system according to claim 1, 2 or 3, in which the bunker conveyor having the crusher has, in the region overlapping the second face conveyor and upstream of the crusher, a screen for direct transfer of the fine-grain portion of the debris to said second conveyor.

5. A system according to any preceding claim in which the feed section of the line loop extends into the mixing tank at that end thereof which is nearer the face conveyor.

6. A system according to any preceding claim in which the bottom of the mixing tank is downwardly inclined from the outlet end of the supply line section of the pipe loop to the entry end of the discharge line section at the opposite end of the mixing tank.

7. A system according to any preceding claim in which the slurry pump is a sludge pump.

8. A system according to any preceding claim in which the end portions of the supply and discharge line sections of the line loop which extend beyond the by-pass line are telescopic tubes which are also part of the unit which follows up the working at relatively long intervals.

9. A system according to any preceding claim in which the content of that length portion of the supply line section which is shut off before the bypass line, as considered in the flow direction, can be forced by the slurry pump by way of the mixing tank in to the discharge line section of the line loop and the content of that length portion of the discharge line section which is shut off after the by-pass line as considered in the flow direction can be discharged into the mixing tank by way of the by-pass line avoiding the slurry pump.

10. A method of advancing that unit of the system of any of claims 1 to 9 which follows the rate of advance at relatively long intervals, with simultaneous lengthening of the supply and discharge line portions of the conveying line, in which method, before the unit advances, first the nearest stationary shut off element in the supply line portion to the rear is closed, and the conveying water trapped in the line portion between the mixing tank and the closure zone discharges into the mixing tank and the corresponding volume is forced into the discharge line section, whereafter the nearest shut-off element of the discharge line portion to the rear is closed and the content present between the closure zone and the mixing tank discharges into the mixing tank, whereafter the emptied portions of the supply and discharge sections of the conveying line are separated and the mixing tank together with the second face conveyor and the line portions remaining connected thereto are' advanced in accordance with the rate of working, whereafter the interrupted conveying lines are reconnected by means of additional pipe sections and of the telescopic tubes.

11. A method according to claim 10 wherein the discharge of the content between the closure zone and the mixing tank, into the mixing tank, is effected with the assistance of the by-pass line and avoiding the siurry pump.

12. A method according to claim 10 or claim 11, wherein the volume of conveying water discharged into the mixing tank after said stationary shut-off element in the supply line portion to the rear has been closed is forced into the discharge line section by means of the slurry pump.

13. A method according to claim 10, 11 or 12 wherein said additional pipe sections are in the form of adaptors.

14. A system according to claim 1 and substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

1 5. A method according to claim 10 and substantially as hereinbefore described with reference to the accompanying drawings.

16. Any novel feature or combination of features described herein.