AU2018200880A1 - System and method for ventilating an underground mine - Google Patents

Abstract

Il:\stp\Interwoven\NRPortbl\DCC\STP\16413178_l.doc-6 02/2018 A system for use in ventilating an underground mine including a working face, the system including: (a) at least one intake airway in fluid communication with intake air and a work area adjacent the working face to supply intake air to the work area; (b) at least one return airway in fluid communication with an exhaust outlet and the work area so that the at least one return airway receives returning air from the work area and supplies this to the exhaust outlet; and, (c) at least one borehole provided downstream of the working face and in fluid communication with the return airway, wherein the at least one borehole is for drawing intake air into the return airway to thereby dilute the return air and provide ventilation. Fig. 2 245 2350,0, 0 25r ~255 o 102 0 250.'o 11-1 255 0 205 250.1' 24Fig 23

Description

SYSTEM AND METHOD FOR VENTILATING AN UNDERGROUND MINE Priority Document [0001] The present application claims priority from Australian Provisional Application No. 2017900377 titled "SYSTEM AND METHOD FOR VENTILATING AN UNDERGROUND MINE" filed on 7 February 2017, the content of which is hereby incorporated by reference in its entirety.

Background of the Invention [0002] The present invention relates to a system and method for use in ventilating an underground mine.

Description of the Prior Art [0003] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

[0004] Underground coal mining can typically be conducted in a two-stage process. An initial development phase typically includes driving a series of roadways, also referred to as headings, in and around coal seams to be mined. These roadways are typically interconnected using a cut-through, whose creation forms pillars of coal. Pillar extraction follows as a second developmental phase, where techniques such as retreating or advancing longwall, or room and pillar extraction are used to recover the coal.

[0005] As an example, longwall mining involves the extraction of coal from a single slice across a working face of a longwall block using hydraulically powered supports. The supports are progressively moved to support a new face as each slice is mined, leaving the previously excavated slice to be allowed to collapse to form a goaf, also referred to as a gob. Previously mined goafs are typically progressively sealed, in order to prevent circulation of flammable and toxic gases, airborne dust, and the like from circulating into current workings. Advantageously, longwall mining therefore requires less investment in permanent support structures as supports are typically portable as mined areas are allowed to collapse.

[0006] Ventilation in the context of this disclosure refers to the air flow around an underground mine, and in particular to ensuring the quality and quantity of air is acceptable. Hazards can arise where ventilation is inadequate, for example, in relation to oxygen content, noxious gases such as methane and carbon dioxide, flammable gases, airborne dust and fumes, products of combustion, humidity and temperature. Resultant safety implications of inadequate ventilation include worker asphyxiation, coal workers' pneumoconiosis (CWP), explosion, spontaneous combustion and the like. Thus, ventilation in an underground mine, including across workings such as the working face, is particularly important.

[0007] Figure 1A shows one example of a prior art ventilation system 100A for an underground coal mine, and more specifically for an underground longwall mine. In this example, the system 100A includes a longwall block 120 also referred to as a longwall panel, including a coal seam to be mined, flanked on one side by two maingate roadways 105 for the introduction of intake air, for example from the surface, and on the opposing side by one tailgate roadway 115 for exhausting return air. Intake air is directed across a working area 110 adjacent the working face of the retreating longwall 125. As the longwall 125 retreats, hydraulic supports supporting the ceiling at the working face are progressively moved, and the ceiling in the previously mined area is allowed to collapse, forming a goaf 130. In this example, the longwall block 120 is adjacent support pillars 135 which separate the current block 120 from a previously mined block, or goaf 140. In any event, the general arrangement shown in Figure 1A is typically referred to as U ventilation. Whilst this arrangement is simple and typically cost effective, U ventilation suffers from a number of disadvantages. For example, the quantity of intake air may be insufficient to adequately manage and dilute gas across the working face, as well as gas expired from the goaf, including seal leakage gas, and gas and fumes emitted from machinery at/adjacent the working face and coal production area.

[0008] A further example of a prior art ventilation arrangement 100B is shown in Figure IB. Features similar to those of the example described above have been assigned correspondingly similar reference numerals. This system 100B utilises a modified U ventilation arrangement including two maingate intakes 105 and a return via the tailgate 115, with the addition of a maingate gas bleed 115B. Whilst this may provide additional drainage of gas from the goaf, potentially flammable gas may be drawn into a mine roadway that would otherwise have much lower levels of flammable gas, creating a larger explosible area and increasing the risk of spontaneous combustion. Additionally, the arrangement 100B may increase respirable dust over the maingate drive.

[0009] A prior art ventilation arrangement 100C, known as Z ventilation, is shown in Figure 1C. In this example, both the maingate roadways 105 and the tailgate roadway 105B are used to supply intake air to the working area 110. Return air 115 is then carried to mains return behind the working face. Whilst Z ventilation 100C provides greater volumes of intake air for gas dilution, it relies on being able to ventilate behind the working face through mined out and broken or subsided ground. In the event resistance of the subsided ground is high, direction of the return air may reverse, directing flammable gas and dust over electrically powered maingate equipment.

[0010] US-3,814,480 describes a method of preventing gas communication between a gas producing formation and a mine passage located therebelow. The method includes the drilling of a well bore into a fracturable rock formation disposed between the gas producing formation and the mine passage. The rock formation is then fractured and the fracture formed thereby is extended to the extent that the shear cracks to be formed by the subsidence of the overburden due to the collapse of the roof of the mine passage during the mining operation will intersect the extended fracture. Gas from the gas producing formation is allowed to flow through the shear cracks in the overburden to and through the fracture to the well bore where it is then vented to the atmosphere or otherwise suitably produced.

[0011] CN-101718208A relates to a ventilating system arranged in U+H shape under the coal mine, in particular to a ventilating systems arranged in U+H shape under the high methane coal mine, aiming at solving the problem of the ventilating system in the process of stopping the face of the coal mine. The ventilating system comprises a stopping face. One side of the stopping face is provided with a belt conveying and air intaking way and an auxiliary conveying and air intaking way in sequence, and the other side is provided with an auxiliary conveying and air intaking way, a first air returning way and a second air returning way in sequence.; The belt conveying and air intaking way and the two auxiliary conveying and air intaking ways intake air and return air after being communicated with the first air returning way and the second air returning way through a channel arranged in front of the stopping face. Therefore, the ventilating system which is arranged in U+H shape and intakes air for three times and returns air for two times is formed.

[0012] Thus, existing ventilation methods and systems suffer from a number of drawbacks, such as expense, and inadequate ventilation, including insufficient noxious gas dilution, inadequate dilution of airborne dust and/or the potential for excessive flammable gas.

Summary of the Present Invention [0013] The present invention seeks to ameliorate one or more of the problems associated with the prior art, or provide a workable alternative.

[0014] In a first broad form the present invention seeks to provide a system for use in ventilating an underground mine including a working face, the system including: a) at least one intake airway in fluid communication with intake air and a work area adjacent the working face to supply intake air to the work area; b) at least one return airway in fluid communication with an exhaust outlet and the work area so that the at least one return airway receives returning air from the work area and supplies this to the exhaust outlet; and, c) at least one borehole provided downstream of the working face and in fluid communication with the return airway, wherein the at least one borehole is for drawing intake air into the return airway to thereby dilute the return air and provide ventilation.

[0015] Typically, the intake airway and return airway are substantially parallel and located on opposing sides of the working face.

[0016] Typically, the intake airway and return airway substantially form a modified U-ventilation system.

[0017] Typically, a first end of the at least one borehole is provided at a surface, and a second end of the borehole is provided downstream of the working face, to thereby draw intake air from the surface.

[0018] Typically, the return airway includes one or more cut-throughs, each of the cut-throughs formed between adjacent pillars at least partially defining an edge of the return airway, and wherein at least one of the boreholes draws intake air into the return airway via at least one of the cut-throughs.

[0019] Typically, each of the at least one boreholes draws intake air into one of the at least one cut-throughs.

[0020] Typically, the second end of the borehole is at least one of: a) substantially equidistant between adjacent pillars; and, b) substantially mid-pillar.

[0021] Typically, the at least one cut-through includes a primary seal to thereby substantially isolate the return airway from a goaf.

[0022] Typically, the at least one cut-through includes: a) a primary seal for substantially isolating an intermediary area from a goaf, the intermediary area in fluid communication with an end of the borehole; and, b) a secondary seal provided between the intermediary area and the return airway, wherein the secondary seal includes a regulator in fluid communication with the return airway and the end of the borehole, the regulator being usable to selectively release intake air from the borehole into the return airway in accordance with a pressure difference across the primary seal.

[0023] Typically, the regulator is openable when the pressure difference is below a threshold, to thereby draw the intake air from the borehole into the return airway.

[0024] Typically, the regulator is closable when the pressure difference is above the threshold, to thereby allow the borehole to operate in an upcasting mode.

[0025] Typically, the borehole is operated in a downcasting mode in advance of the working face to thereby provide dilution of return air, and in an upcasting mode behind the working face to thereby at least partially drain gas.

[0026] Typically, the system includes at least one blower in fluid communication with at least one of the boreholes, to thereby actively control flow of the intake air.

[0027] Typically, the borehole is biased towards the return airway.

[0028] Typically, the borehole receives a supply of an inerting agent to thereby minimise a risk of combustion.

[0029] Typically, the system includes at least one radiator and at least one surface heat exchanger in communication with the at least one borehole to thereby provide cooling to the working face.

[0030] Typically, the boreholes are any one of lined and at least partially unlined.

[0031] Typically, the intake airway and return airway form opposing sides of a block, the block including the working face.

[0032] Typically, the intake airway is formed in a maingate roadway, and the return airway is formed in a tailgate roadway.

[0033] Typically, the working face includes a longwall working face.

[0034] Typically, the longwall working face is retreating.

[0035] Typically, a diameter of the borehole is at least one of: a) between 12 inches and 24 inches; b) between 15 inches and 22 inches; c) between 17.5 inches and 18 inches; d) 17.75 inches; and, e) about 450 mm.

[0036] In a second broad form the present invention seeks to provide a method for ventilating an underground mine, the underground mine including a working face and a work area adjacent the working face, wherein the method includes: a) directing intake air from an intake airway to the work area; b) returning return air from the work area via a return airway to an exhaust outlet; and, c) directing intake air from a borehole downstream of the working face into the return airway, to thereby dilute the return air and provide ventilation.

Brief Description of the Drawings [0037] An example of the present invention will now be described with reference to the accompanying drawings, in which: - [0038] Figure 1A is a schematic diagram of an example of a prior art underground mine ventilation system including U ventilation; [0039] Figure IB is a schematic diagram of an example of a prior art underground mine ventilation system including U ventilation with a maingate gas bleed; [0040] Figure 1C is a schematic diagram of an example of a prior art underground mine ventilation system including Z ventilation; [0041] Figure 2 is a schematic diagram of a first example of a system for use in ventilating an underground mine; [0042] Figure 3 is a flowchart of a further example of a method for use in ventilating an underground mine; and, [0043] Figure 4 is a schematic diagram of further example of a system for use in ventilating an underground mine.

Detailed Description of the Preferred Embodiments [0044] An example of a system for use in ventilating an underground mine including a workface will now be described with reference to Figure 2.

[0045] For the purpose of these examples, it is assumed that the systems for use in ventilation are performed as part of an underground mine including a working face defined by a retreating longwall. However, it will be appreciated that the systems and methods herein could in practice be performed in an underground mine employing any other suitable mining technique, such as an advancing longwall or room and pillar extraction, and reference to longwall is not intended to be limiting.

[0046] In this example, the system 200 includes two intake airways 205 in fluid communication with intake air and a work area 210 adjacent the working face to supply intake air to the work area 210. Whilst two intake airways 205 are included in this example, it will be appreciated that any number of intake airways 205 may be used, for example one or more intake airways 205.

[0047] Reference to “intake air” in the context of this disclosure includes any suitable air for providing ventilation, for example, ambient air from a surface above a mine, which may be passively directed into the mine via one or more airways, and/or may be at least partially controlled using devices such as one or more fans, booster or auxiliary fans, heat exchangers, cooling devices, or the like. Moreover, intake airways 205 could refer to any suitable conduit for conducting the flow of intake air, such as one or more roadways, pipes, shafts, or the like.

[0048] The system 200 further includes one or more return airways 215 in fluid communication with an exhaust outlet and the work area 210, so that the at least one return airway 215 receives returning air from the work area and supplies this to the exhaust outlet.

[0049] Reference to “return air” in the context of this disclosure includes air and/or gas which is to be exhausted, for example, in the event the return air has passed over workings and may have entrained noxious and/or flammable gases, airborne particles, and the like. Furthermore, return airway(s) 215 refers to any suitable airway for conducting return air, such as one or more roadways, pipes, conduits, shafts, or the like. Moreover, the exhaust outlet includes any suitable outlet for exhausting return air, such as a surface end of the return airway 215, or an outlet which is in fluid communication with the return airway 215 and the surface, or the like.

[0050] Additionally, the system 200 includes one or more boreholes 250.1 provided downstream of the working face and in fluid communication with the return airway 215, where the borehole(s) 250.1 are for drawing intake air into the return airway to thereby dilute the return air and provide ventilation. Typically the boreholes are provided by drilling from the surface into the return airway 215, or an airway, shaft, pipe, conduit, or the like, in fluid communication with the return airway 215. However, this is not essential and any suitable method of providing the boreholes downstream of the working face may be used. Moreover, in the context of this disclosure the term “drawing” may include either passive or active direction or control of air. For example, the intake air may be passively drawn by the borehole(s) and/or may be at least partially controlled using one or more fans, blowers, radiators, or the like.

[0051] In any event, the above described system 200 is particularly advantageous, as intake air supplied by the borehole(s) 250.1 provides additional dilution of return gas, allowing for the management of noxious and/or flammable gases, such as methane, thus minimising the risk of an explosion hazard. Moreover, as intake air is introduced into the return airway 215 by the borehole(s) 250.1, and not as higher quantities of intake airflow over the working face, the system 200 offers increased gas dilution in the return airway without increasing respirable dust on the working face.

[0052] This is particularly salient, as attempting to increase gas dilution in the return airway 215 is conventionally achieved through an increase in the quantity of intake air via the intake airways 205. However, this in turn may increase the quantity of respirable dust across the working face. So whilst a minimisation of explosion risk may be achieved, it is at the cost of an increased risk of CWP, also referred to as “black lung”. Thus, the above described system 200 provides a simple and cost effective arrangement for providing return airway dilution and minimising explosion risk without necessarily increasing intake air quantities across the working face or risk of CWP.

[0053] In addition to the above, the system 200 herein provides mitigation for gas accumulation near the tailgate drive electrics and machinery, which can pose a petrol ignition and explosion hazard, and gas and dust accumulations in the coal production area, which can also create an ignition and explosion hazard.

[0054] Advantageously, increasing dilution of gas in the return airway in turn can enable improved access into the return airway. For example, diesel powered vehicle access is typically prohibited to tailgate roadways, or return airways, as the concentration of flammable gas poses a significant explosion risk. By increasing the dilution through the use of boreholes in fluid communication with the return airways, this in turn decreases the concentration of flammable gas and hence the ignition risk posed by vehicles. Similarly, the concentrations of noxious gases and asphyxiates in the return airway are also decreased, lowering the risk posed to any worker accessing the tailgate or return airway.

[0055] Furthermore, the borehole(s) can optionally be utilised for additional uses such as gas drainage after the longwall has retreated and/or for application of an inerting material, and this will be discussed further below.

[0056] A number of further features will now be described.

[0057] In this example, the intake airways 205 and the return airway 215 are substantially parallel and located on opposing sides of the working face. Beneficially, for example, this allows the intake and return airways 205, 215 to operate in advance of the working face, and hence the system 200 may not be reliant on intake or retum/drainage through broken or subsided ground that may provide inadequate permeability.

[0058] The intake airways 205 and return airway 215 may in some examples form opposing sides of a block 220, also referred to as a panel, where the block 220 includes the working face. This can be typical in systems 200 utilised in respect of a retreating longwall, as the panel in this example refers to a longwall panel which is progressively mined in successive slices, or working faces. Thus, in some examples the working face includes a longwall working face, and more typically the longwall working face is retreating.

[0059] Consequently, in some instances, such as the example shown in Figure 2, the intake airways 205 and the return airway 215 substantially form a modified U-ventilation system. That is, the configuration of the intake airways 205 and the return airway 215 is such that it utilises U ventilation, however the system 200 additionally employs the borehole(s) as described. Thus, the system 200 may capture the advantages of U-ventilation, such as simplicity and cost-effectiveness, whilst also mitigating the risks posed by high concentrations of noxious and flammable gases in the return airway.

[0060] Typically, the intake airways 205 are formed in a maingate roadway, also referred to as a maingate or main gate, and the return airway 215 is formed in a tailgate roadway, also referred to as a tailgate or tail gate. However, this is not essential and in other examples the airways may be formed in any suitable arrangement, for example using pipes, shafts, headings, or the like.

[0061] In some examples, a first end of the at least one borehole 250.1 is provided at a surface, and a second end of the borehole is provided downstream of the working face, to thereby draw intake air from the surface. In this regard, the surface typically refers to the surface at ground level, or alternatively may refer to any other surface or area which is exposed to sufficient quality air for the purposes of providing intake air, such as a fan or blower outlet, cooling device outlet, or the like. Such a borehole 250.1 may be provided in any manner of ways, including drilling from the surface, for example using known drilling techniques.

[0062] As will be appreciated, the direction of a borehole 250, and hence the position of a terminating or second end of borehole 250, may deviate when drilling from the surface. This may occur for any number of reasons, including imprecision in planning coordinates, incorrect drilling/hammering pressure, the type and composition of strata being drilled, or the like. In such examples, the second end of the borehole 250 may be typically fluidly connected to its intended position in the mine via additional pipes, conduits, shafts, or the like. Accordingly, reference to a borehole 250 end positioning is not intended to be limiting.

[0063] In one example, the return airway 215 includes one or more cut-throughs, each of the cut-throughs formed between adjacent pillars 235 at least partially defining an edge of the return airway 215, where at least one of the boreholes 250.1 draws intake air into the return airway 215 via at least one of the cut-throughs. Beneficially, this allows ends of the boreholes to be positioned above the cut-throughs, rather than directly overhead in the return airways, minimising potential overhead hazards such as from falling objects or a collapsing borehole. However, this is not essential.

[0064] In any event, the arrangement of pillars 235 and cut-throughs defining an edge of the return airway 215 may be achieved in any suitable manner, however typically the return airway 215 is formed from an intake airway which previously serviced the adjacent mined panel, or adjacent goaf 240. For example, the intake airways 215 in this example are formed from two substantially parallel airways which are interconnected by a series of cut-throughs, providing intermediary access, where the cut-throughs form a series of pillars 245 therebetween. As the current block 220 is mined, and the working face retreats, the intake airways 205 nearest the current panel 220 progressively collapse into the goaf 235. Additionally, the cut-throughs may be progressively sealed 255 in order to minimise noxious and flammable gas, and dust leakage from the goaf 235 into the workings. Thus the remaining intake airway 205 forms the return airway for subsequent mining of another adjacent longwall panel with the pillars 245 and cut-throughs at least partially defining its edge.

[0065] Typically, each of the one or more boreholes 250 in this example draws intake air into one of the one or more cut-throughs, and more typically the boreholes 250 are provided in an arrangement of one per pillar, and/or one per cut-through. However, this is not essential, and the number of boreholes 250 may be determined according to cost constraints and/or dilution requirements.

[0066] In some examples, the second end of the borehole(s) 250 is substantially equidistant between adjacent pillars 235 and/or substantially mid-pillar. In this regard, mid-pillar typically refers to a position in the cut-though which is substantially equidistant from opposing ends of the cut-through, which corresponds to opposing faces of an adjacent pillar 235. This is particularly advantageous as a mid-pillar arrangement reduces abutment loading and a risk of borehole collapse. However, this is not essential, and in other examples the second end of the borehole(s) 250 may be, for example, moved or biased toward the return airway 215 and piped to mid-pillar, or the like.

[0067] Additionally or alternatively, the at least one cut-through may include one or more primary seals 255 which thereby substantially isolate the return airway 215 from a goaf 240. As described above, sealing of the goaf may be required in order to minimise the risk of toxic or flammable gas or airborne dust drainage from the previously mined ground defined by the goaf 240 into the workings of the mine.

[0068] In one example, at least one of the cut-throughs includes a primary seal 255 for substantially isolating an intermediary area from a goaf 240, where the intermediary area includes an end of the borehole 250 and/or where the intermediary area is in fluid communication with the end of the borehole 250. Additionally, the cut-through includes a secondary seal provided between the intermediary area and the return airway 215, where the secondary seal includes a regulator in fluid communication with the return airway 215 and the end of the borehole 250. In this regard, the regulator is usable to selectively release intake air from the borehole 250 into the return airway 215 in accordance with a pressure difference across the primary seal 255. Accordingly, the regulator may include any suitable device, including a resealable hatch, valve, or the like.

[0069] Thus, for example, intake air from the borehole 250 may be selectively released into the return airway 215 when the pressure difference across the primary seal 255 is of an acceptable level, e.g. it falls within a predetermined range of values. As will be appreciated, the predetermined range of values may be determined in accordance with regulations or usage guidelines associated with the primary seal 255 or as supplied by the seal manufacturer or the like. In the event the pressure difference falls outside of the predetermined range, the secondary seal may be sealed in order to prevent airflow from the borehole 250 into the return airway 215. Optionally, in this regard the borehole 250 may operate in an upcasting mode to vent air accumulating in the intermediary area to the surface.

[0070] Pressure differences across goaf seals, such as the primary seal 255, are typically required to be monitored in order to meet regulations and/or manufacturing requirements so as to minimise the risk of gas leakage from the goaf 240. In the event pressure behind the goaf 240 exceeds pressure in the intermediary area, there is a risk of gas leakage across the seal from the goaf 240 into the return airway 215, which can pose an explosion risk. Thus by selectively sealing the secondary seal and venting air in the intermediary area when gas leakage may be present, this effectively reduces the risk of gas leaking from the goaf 240 into the return airway 215, in turn reducing the explosion risk.

[0071] Optionally, the regulator may be openable when the pressure difference is below a threshold, to thereby draw the intake air from the borehole 250 into the return airway 215. In this context, the pressure difference will typically include the difference as determined in the direction from the goaf 240 across the primary seal 255 to the intermediary area. In this instance, when the pressure difference is below the threshold, the risk of gas leakage may be minimal, or deemed acceptable according to predetermined standards or regulations, and therefore intake air is draw from the borehole 250 into the return airway 215. The threshold may be determined in any suitable manner, for example, in consultation with relevant regulations, manufacturing guidelines associated with the primary seal 255, in accordance with acceptable gas leakage levels, or the like.

[0072] Additionally, the regulator may be closed when the pressure difference is above the threshold, to thereby allow the borehole 250 to operate in an upcasting mode. For example, when the pressure in the goaf 240 exceeds the pressure in the intermediary area by an unacceptable level, this may indicate a high risk of primary seal gas leakage. Therefore, the borehole 250 can provide exhaustion of potentially leaked gas from the intermediary area to the surface when the regulator is closed.

[0073] Whilst in the examples above, reference is made to the intermediary area including an end of the borehole, in some instances, due to drilling inaccuracies the end of the borehole may fall outside of the intermediary area. In this case, the end of the borehole may be provided in fluid communication with the intermediary area using pipes, conduits, or the like. Therefore, reference to the end of the borehole in the intermediary area is not intended to be limiting.

[0074] Optionally, one or more of the boreholes 250 may be biased towards the return airway 215. For example, it may be advantageous to bias the boreholes 250 in the event they are created (such as drilled) after longwall extraction of an adjacent block (for example, after formation of the adjacent goaf 240). In this regard, biasing of the boreholes 250 may ensure a second end of the borehole is advanced away from the adjacent goaf 240 and toward more stable ground. Alternatively, one or more of the boreholes may be drilled prior to adjacent longwall extraction. In this instance, it may be more beneficial to provide the second end of the borehole substantially mid-pillar, as discussed above, in order to reduce abutment loading and likelihood of borehole collapse.

[0075] Additionally or alternatively, one or more of the boreholes 250 may receive a supply of an inerting agent to thereby minimise a risk of combustion. As the boreholes 250 provide surface access to the workings of a mine, even after retreat of an adjacent panel, this allows for inerting agent to be remotely distributed. In the example of an underground coal mine, the inerting agent may include stone dust or calcium carbonate, which is used in the prevention of coal dust explosions. In a process referred to as “stonedusting”, stone dust or calcium carbonate may be applied to previously mined areas in order to render coal dust clouds inert, and minimise explosion risk. However, the application of stone dust can create large quantities of airborne dust which is hazardous in confined spaces such as mine workings, therefore remote supply is particularly beneficial. Moreover, stonedusting is typically performed more than once, in order to ensure adequate inerting agent is available as coal dust continues to accumulate, therefore remote application saves considerable time in obviating the need for obtaining periodic underground access where diesel vehicle access is limited by gas.

[0076] In one example, the system 200 includes one or more radiator, such as high pressure radiators, and one or more surface heat exchangers in communication with the at least one borehole 250 to thereby provide cooling to the working face. For example, cooling fluid such as water, coolant, or the like, may be chilled on the surface using the heat exchanger, piped underground via the borehole 250, and pass through the radiator(s) to thereby transfer cooling into the workings. The resultant fluid can then be returned to the heat exchangers at the surface for chilling and recirculation, for example, using a closed loop arrangement. This is particularly advantageous as temperature regulation is important for health and safety of workers. In fact, such an arrangement may be utilised in providing cooling or spot cooling to any suitable area of the return airway 215 via one or more of the boreholes 250, as required. In some examples, as discussed above, boreholes 250 may be drilled prior to the adjacent longwall extraction 140. Accordingly, such pre-drilled boreholes 250 are in fluid communication with the intake airways of the adjacent longwall 140. Consequently, spot cooling or cooling may be provided to at least part of the intake airway(s) using one or more pre-drilled borehole(s) 250 in a similar manner.

[0077] One or more of the boreholes 250 may be lined or at least partially unlined, for example unlined below a tertiary casing. In this regard, a lined or at least partially unlined borehole may be selected in accordance with the strata in which the borehole is located.

[0078] A diameter of one or more of the boreholes may, in some examples, typically be between about 12 inches and 24 inches, more typically between 15 inches and 22 inches, more typically between 17.5 inches and 18 inches, most typically 17.75 inches, and/or about 450 mm. In this regard, the selection of borehole diameter may be in accordance with factors such as budget considerations in terms of drilling costs, as well as dilution requirements such as the quantity of additional intake air required in the return airway for adequate ventilation, gas dilution and the like.

[0079] Optionally, the borehole(s) 250.1 may be operated substantially in a downcasting mode in advance of the working face to thereby provide dilution of return air, and the borehole(s) 250.2 may be operated in an upcasting mode behind the working face to thereby at least partially drain gas. In the context of this disclosure, downcasting mode refers to either active or passive control of airflow from the surface into the workings, and upcasting mode refers to either active or passive control of airflow from the workings to the surface. Advantageously, this allows boreholes 250.2 to be repurposed, for example, after the longwall working face has retreated past, as a means to drain noxious and flammable gas and/or airborne dust such as coal dust from the goaf 230. This is a particularly cost effective method of providing both return airway 215 dilution and subsequent goaf gas drainage utilising the same boreholes 250.

[0080] In one example, the system 200 may include a blower, fan, or the like, in fluid communication with the borehole(s) 250.1, 250.2 in order to control the flow of intake air via the borehole(s) 250.1, 250.2. For example, the blower may be configured to force additional intake air into the return airway 215 via the blowhole 250.1 during downcasting mode, and to force additional return air out of the goaf 235 during upcasting mode. In one particular example, a borehole 250.1 adjacent to, or immediately downstream of, the work area defined by a current working face, such as adjacent to the working face machinery, outbye of a tailgate drive, or the like, may be in communication with a blower operated to actively force intake air at high pressure while the current working face is worked. Beneficially, this actively dilutes gas at the tailgate drive machinery and reduces the risk of ignition. After the working face retreats, the blower is operated to actively force return air from the borehole 250.1 in order to extract flammable and noxious air from the subsequent goaf 235.

[0081] For example, to introduce additional intake air outbye of the tailgate drive for gas dilution, active high pressure force ventilation can be used to push ventilation down a first borehole 250.1, such as, at about four times ambient pressure. Thus, the blower may be used in a forcing arrangement until the longwall passes the cut-through, where the blower is switched to a suction/extraction system to draw air and gas.

[0082] Additionally or alternatively, the system 200 may include a maingate bleed. In this regard, boreholes 250 drilled prior to the adjacent longwall extraction 140, which are in fluid communication with the intake airways of the adjacent longwall 240, may be used to draw return air in a maingate bleed arrangement when extracting the adjacent longwall panel 240, for example, after the adjacent longwall face has retreated past. Subsequently, the same boreholes 250 may be utilised to direct intake air into the return airway 215 when extracting the current longwall panel 220.

[0083] In a particular example, a maingate bleed, which is typically high purity and low flow, may be provided into a pipe range to the surface and/or via an airway. This allows for a maingate regulator (in the airway between the longwall face and the bleed point) that is retreated less frequently (in one example, once every two or three pillars and may be several pillars behind the longwall) and is allowed to operate at lower pressures, therefore providing a simplified system. Additionally, improvements in explosion and spontaneous combustion risks may be realised by drawing the inert low-oxygen atmosphere fringe forward.

[0084] An example of a method for ventilating an underground mine will now be described with reference to Figure 3. In this example, the underground mine includes a working face and a work area adjacent the working face.

[0085] At step 300, the method includes drawing intake air from an intake airway to the work area. At step 310, the method includes returning return air from the work area via a return airway to an exhaust outlet. Intake air is directed from a borehole downstream of the working face into the return airway at step 320, to thereby dilute the return air and provide ventilation.

[0086] This method is particularly advantageous in minimising the risk of explosion in the return airway by increasing return air dilution, whilst maintaining the quantity of intake air flowing across the working face at acceptable levels so as not to increase airborne dust and the risk of CWP for workers operating the work area.

[0087] Moreover, the method may include any of the additional features described herein.

[0088] A further example of a system for use in ventilating an underground mine will now be described with reference to Figure 4. Features similar to those of the example in Figure 2 described above have been assigned correspondingly similar reference numerals.

[0089] In this example, the system 400 includes a cut-through defined between adjacent pillars 235 which includes a primary seal 255 for substantially isolating an intermediary area from the goaf 240. In addition, the cut-through includes a secondary seal 410 provided between the intermediary area and the return airway 215, where an end of the borehole 250 is in fluid communication with the intermediary area.

[0090] Whilst in this example, the end of the borehole 250 terminates in the intermediary area, it will be appreciated that in other examples the end of the borehole 250 may terminate outside of the intermediary area, such as, due to inaccuracies in the drilling process. In this case, the end of the borehole 250 may be fluidly connected to the intermediary area using any suitable connection such as one or more pipes, conduits, shafts, or the like.

[0091] The secondary seal or stopping 410 includes a resealable hatch or valve 420 in fluid communication with the return airway 215 and the borehole 250. In this example, the primary and secondary seals 255, 410 and the intermediary area form a balance chamber, whereby the pressure difference across 430 can be managed by monitoring and adjusting flow through the borehole 250 and the resealable hatch 420.

[0092] In use, in the event pressure of the goaf 240 exceeds pressure in the intermediary area of the balance chamber, namely a positive primary seal pressure difference 430 exists, goaf gas has the potential to leak across the primary seal 255. Thus, when the primary seal pressure difference 430 reaches a predetermined threshold, the resealable hatch 420 is sealable in order to vent any potential leaked gas to the surface via borehole 250, hence the borehole 250 is operable in an upcasting mode.

[0093] Conversely, when the primary seal pressure difference 430 falls under a predetermined threshold, and thus the risk of goaf gas leakage is deemed acceptable, the resealable hatch 420 is openable to allow intake air to flow from the surface into the return airway 215 via the borehole 250 operating in a downcasting mode.

[0094] Accordingly, the system 400 provides a particularly effective method of controlling gas leakage across a seal by selectively draining leakage gas via the borehole 250 when goaf pressure is too high, and diluting return air in the return airway when goaf pressure is acceptable.

[0095] In one example, the primary seal 255 is constructed to comply with relevant regulations in relation to goaf seals, however this is not essential. Additionally or alternatively, the secondary seal 410 may include any suitable arrangement, such as a stopping, or the like, and in some instances the secondary seal 410 may not be as highly rated as the primary seal 255.

[0096] A further specific example of a ventilation system and method for use in ventilating a mine will now be described. In particular, the system in this example includes: • Multiple downcast boreholes in a longwall tailgate. Typically, one borehole is provided per pillar and located in the cut-through between the seal and the tailgate roadway. These boreholes are used to draw intake air into the workings and dilute flammable gas. • The boreholes may be lined or unlined below tertiary casing. • In the event the boreholes are drilled prior to longwall extraction, the boreholes may be drilled as close as practical to mid pillar to reduce abutment loading and the likelihood of hole collapse. Alternatively, if the boreholes are drilled post longwall extraction of the adjacent block, the holes may be biased towards the tailgate roadway to move it towards stable ground. • The borehole diameter may be determined by optimizing drilling conditions and mine depth against intake flowrate. Borehole diameter may therefore vary typically from 12" to 24", although more typically the largest single pass method may be most economical and the hole size may be around 17.75" (-450mm). • As the longwall retreats past a borehole, the boreholes may be used as goaf drainage holes, for example by operating them in an upcasting mode. This may improve capture efficiency by capturing the goaf edge void and seal leakage gas that may otherwise not be captured by conventional goaf drainage and otherwise reported to the ventilation system. • As the longwall first passes the tailgate cut-through, the mine may employ a purpose designed high pressure blower to extract gas. This gas it typically managed to stay outside flammable ranges.

[0097] Beneficially, the above described system enables the management of return methane concentrations using a modification of the standard U ventilation system (for example, methane contained in face gas, goaf gas and via seal leakage), which has less operational constraints than for example a Z ventilation system. Additionally, the system of this example enables management of flammable gas adjacent to the tailgate to reduce methane concentrations against the tailgate drive (which can be form an explosion hazard).

[0098] Optionally, a number of adaptations may be used in this system in order to provide additional benefit, such as: • operating one or more of the boreholes to stonedust the longwall return remotely from the surface; • using balance chambers and regulated intake pressures in conjunction with one or more of the borehole(s) to manage and reduce seal leakage (and in one example, similar to the VCD described in respect of Figure 4); and, • using high pressure radiators coupled to surface heat exchangers in fluid communication with the borehole(s) to enable underground spot cooling.

[0099] Advantageously, the above described system includes safety benefits, for example: • a simplified VCD construction process around longwall; • increased gas dilution in the longwall return roadway without creating respirable dust problems on the longwall face; • ability to improve goaf drainage capture efficiency, therefore reducing the amount of gas reporting to the mine's ventilation system and increasing the percentage able to be used for power generation and/or greenhouse gas emissions reduction; • optionally the incorporation of a simple, safe and cost effective means of introducing stonedust as a means of coal dust explosion prevention; and, • optionally incorporates a design which can be used to manage seal pressures and gas leakage, thus improving improves flammable gas levels in return roadways (a safety risk that potentially increases costs by limiting production to statutory gas levels), and reducing the hazard of potentially explosible concentrations of gas and the spontaneous combustion risk in adjacent sealed goaf areas.

[0100] In this example, it is typically assumed that surface access for drillings into the workings is available, and that suitable drilling technology and drilling conditions allow for drilling into the workings. Typically, lightning protection may be considered separately, for example, in accordance with a mine's Safety & Health Management Systems.

[0101] In any event, the examples described herein describe a method and system for use in ventilating an underground mine, and additionally a ventilation control device, which advantageously offers a simple and cost effective method for diluting return air. Thus, for example, this reduces noxious and flammable gas concentrations in return airways, reducing the risk of spontaneous combustion.

[0102] Throughout this specification and claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers.

[0103] Persons skilled in the art will appreciate that numerous variations and modifications will become apparent. All such variations and modifications which become apparent to persons skilled in the art, should be considered to fall within the spirit and scope that the invention broadly appearing before described. Thus, for example, it will be appreciated that features from different examples above may be used interchangeably where appropriate.

Claims (23)

1. THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1) A system for use in ventilating an underground mine including a working face, the system including: a) at least one intake airway in fluid communication with intake air and a work area adjacent the working face to supply intake air to the work area; b) at least one return airway in fluid communication with an exhaust outlet and the work area so that the at least one return airway receives returning air from the work area and supplies this to the exhaust outlet; and, c) at least one borehole provided downstream of the working face and in fluid communication with the return airway, wherein the at least one borehole is for drawing intake air into the return airway to thereby dilute the return air and provide ventilation.
2. 2) A system according to claim 1, wherein the intake airway and return airway are substantially parallel and located on opposing sides of the working face.
3. 3) A system according to any one of the claims 1 and 2, wherein the intake airway and return airway substantially form a modified U-ventilation system.
4. 4) A system according to any one of the claims 1 to 3, wherein a first end of the at least one borehole is provided at a surface, and a second end of the borehole is provided downstream of the working face, to thereby draw intake air from the surface.
5. 5) A system according to any one of the claims 1 to 4, wherein the return airway includes one or more cut-throughs, each of the cut-throughs formed between adjacent pillars at least partially defining an edge of the return airway, and wherein at least one of the boreholes draws intake air into the return airway via at least one of the cut-throughs.
6. 6) A system according to claim 5, wherein each of the at least one boreholes draws intake air into one of the at least one cut-throughs.
7. 7) A system according to claim 5 or claim 6, wherein the second end of the borehole is at least one of: a) substantially equidistant between adjacent pillars; and, b) substantially mid-pillar.
8. 8) A system according to any one of the claims 5 to 7, wherein the at least one cut-through includes a primary seal to thereby substantially isolate the return airway from a goaf.
9. 9) A system according to any one of the claims 5 to 8, wherein the at least one cut-through includes: a) a primary seal for substantially isolating an intermediary area from a goaf, the intermediary area in fluid communication with an end of the borehole; and, b) a secondary seal provided between the intermediary area and the return airway, wherein the secondary seal includes a regulator in fluid communication with the return airway and the end of the borehole, the regulator being usable to selectively release intake air from the borehole into the return airway in accordance with a pressure difference across the primary seal.
10. 10) A system according to claim 9, wherein the regulator is openable when the pressure difference is below a threshold, to thereby draw the intake air from the borehole into the return airway.
11. 11) A system according to claim 10, wherein the regulator is closable when the pressure difference is above the threshold, to thereby allow the borehole to operate in an upcasting mode.
12. 12) A system according to any one of the claims 1 to 11, wherein the borehole is operated in a downcasting mode in advance of the working face to thereby provide dilution of return air, and in an upcasting mode behind the working face to thereby at least partially drain gas.
13. 13) A system according to any one of the claims 1 to 12, wherein the system includes at least one blower in fluid communication with at least one of the boreholes, to thereby actively control flow of the intake air.
14. 14) A system according to any one of the claims 1 to 13, wherein the borehole is biased towards the return airway.
15. 15) A system according to any one of the claims 1 to 14, wherein the borehole receives a supply of an inerting agent to thereby minimise a risk of combustion.
16. 16) A system according to any one of the claims 1 to 15, wherein the system includes at least one radiator and at least one surface heat exchanger in communication with the at least one borehole to thereby provide cooling to the working face.
17. 17) A system according to any one of the claims 1 to 16, wherein the boreholes are any one of lined and at least partially unlined.
18. 18) A system according to any one of the claims 1 to 17, wherein the intake airway and return airway form opposing sides of a block, the block including the working face.
19. 19) A system according to any one of the claims 1 to 18, wherein the intake airway is formed in a maingate roadway, and the return airway is formed in a tailgate roadway.
20. 20) A system according to any one of the claims 1 to 19, wherein the working face includes a longwall working face.
21. 21) A system according to claim 20, wherein the longwall working face is retreating.
22. 22) A system according to any one of the claims 1 to 21, wherein a diameter of the borehole is at least one of: a) between 12 inches and 24 inches; b) between 15 inches and 22 inches; c) between 17.5 inches and 18 inches; d) 17.75 inches; and, e) about 450 mm.
23. 23) A method for ventilating an underground mine, the underground mine including a working face and a work area adjacent the working face, wherein the method includes: a) directing intake air from an intake airway to the work area; b) returning return air from the work area via a return airway to an exhaust outlet; and, c) directing intake air from a borehole downstream of the working face into the return airway, to thereby dilute the return air and provide ventilation.