Ducting system

Abstract

The present invention relates to a ducting system (100) for conveying a flow of a gaseous feed (110) comprising a combustible component from an inlet to at least one combustion module (12), the ducting system (100) utilising a combination of a sensor (C0) for measuring the concentration of the combustible component in the gaseous feed (110), a flame detector (F0, F1, F2, F3, . . . , Fn) a shut-off valve (6) and a flame arrestor (5) located in a flow path of the gaseous feed upstream of the shut-off valve (6) such that a measurement of a concentration of combustible material in the gaseous feed over a specified concentration by the sensor (CO) causes the shut-off valve (6) to be configured to the closed position for preventing flow of a gaseous feed comprising a combustible mixture of the combustible component from reaching an ignition source and/or detection of flame by the flame detector (F0, F1, F2, F3, . . . , Fn) causes shut-off valve (6) to be configured to the closed position for attenuating propagation of a flame towards the inlet.

Claims

1. A ducting system for conveying a flow of a gaseous feed of ventilation air derived from a coal mine comprising a combustible component from an inlet to at least one combustion module, the system comprising: a shut-off valve configurable to have an open position to allow the flow of the gaseous feed from the inlet to the at least one combustion module and a closed position to prevent the flow of the gaseous feed from the inlet to the at least one combustion module; a sensor to measure a concentration of the combustible component in the flow of the gaseous feed, the sensor located upstream of the shut-off valve; a flame detector located downstream of the shut-off valve; a flame arrestor located in a flow path of the gaseous feed upstream of the shut-off valve; and a source of fire retardant and a fire retardant valve feeding one or more fire retardant injection points for controlling flow of the fire retardant into the ducting system, the one or more fire retardant injection points positioned between the flame arrestor and the at least one combustion module, wherein the shut-oft valve is operatively associated with the sensor such that a measurement of a concentration of the combustible component in flow of the gaseous feed over a specified concentration by the sensor causes the shut-off valve to be configured to the closed position for preventing flow of a gaseous feed comprising a combustible mixture of the combustible component from reaching an ignition source, wherein the specified concentration is 1.25% methane as the combustible component wherein the shut-off valve is operatively associated with the flame detector such that detection of flame by the flame detector causes the shut-off valve to be configured to the closed position for attenuating propagation of a flame toward the inlet, and wherein the fire retardant valve is operatively associated with the flame detector such that detection of flame by the flame detector causes the fire retardant valve to open allowing the tire retardant to flow into the ducting system for attenuating the detected flame; further comprising a supplementary gaseous feed comprising a supplementary combustible component and a supplementary gaseous feed valve for controlling flow of supplementary gaseous feed into the flow of the gaseous feed downstream of the shut-off valve, wherein the supplementary gaseous feed is in fluid communication with a gas mixer for mixing the gaseous feed with the supplementary gaseous feed.

2. A ducting system for conveying a flow of a gaseous feed of ventilation air derived from a coal mine comprising a combustible component from an inlet to at least one combustion module, the system comprising: a sensor to measure a concentration of the combustible component in the flow of the gaseous feed; a flame detector; a shut-off valve configurable to have an open position to allow the flow of the gaseous feed from the inlet to the at least one combustion module and a closed position to prevent the flow of the gaseous feed from the inlet to the at least one combustion module; and a flame arrestor located in a flow path of the gaseous feed upstream of the shut-oft valve, wherein the shut-off valve is operatively associated with the sensor such that a measurement of a concentration of the combustible component in flow of the gaseous feed over a specified concentration by the sensor causes the shut-off valve to be configured to the closed position for preventing flow of a gaseous feed comprising a combustible mixture of the combustible component from reaching an ignition source, wherein the specified concentration is 1.25% methane as the combustible component; and wherein the shut-off valve is operatively associated with the flame detector such that detection of flame by the flame detector causes the shut-off valve to be configured to the closed position for attenuating propagation of a flame toward the inlet; further comprising a supplementary gaseous feed comprising a supplementary combustible component and a supplementary gaseous feed valve for controlling flow of supplementary gaseous feed into the flow of the gaseous feed downstream of the shut-off valve, wherein the supplementary gaseous feed is in fluid communication with a gas mixer for mixing the gaseous feed with the supplementary gaseous feed.

3. The system according to claim 2, wherein the sensor is located between the inlet and the shut-off valve at a position such that the shut-off valve can be configured to the closed position prior to a portion of the gaseous feed, comprising the combustible component at a concentration over the specified concentration as measured by the sensor, flowing to the shut-off valve.

4. The system according to claim 3, wherein the first sensor is positioned proximal to a source of the gaseous feed.

5. The system according to claim 2, wherein the at least one combustion module is shut down to remove the combustion module as a potential ignition source upon measurement of a concentration of the combustible component in the flow of the gaseous feed over the specified concentration by the sensor and/or detection of flame by the flame detector.

6. The system according to claim 2, further comprising a combustion module flame arrestor located proximal each of the at least one combustion modules.

7. The system according to claim 2 wherein the flame arrestor comprises a crimped metal ribbon flame arrestor element.

8. The system according to claim 7, wherein the crimped metal ribbon flame arrestor element has an expansion ratio greater than 1.

9. The system according to claim 7, wherein the crimped metal ribbon flame arrestor element comprises a path length of from 10 mm to 250 mm.

10. The system according to claim 2, further comprising a first source of fresh air and a first fresh air valve for controlling flow of the first source of fresh air into the ducting system, wherein the first fresh air valve is operatively associated with the shut-off valve such that when the shut-off valve is configured to the closed position, the first fresh air valve is in an open position to allow flow of fresh air into the system for diluting the concentration of the combustible component.

11. The system according to claim 2, wherein at least one fire retardant injection point is positioned upstream of the shut-off valve and at least one fire retardant injection point is positioned downstream of the shut-off valve.

12. The system according to claim 2, further comprising one or more burst panels located upstream of the at least one combustion module and downstream of at least one fire retardant injection point.

13. The system according to claim 2, further comprising a second source of fresh air and a second fresh air valve for controlling flow of the second source of fresh air into the flow of the gaseous feed at a position upstream of the mixer.

14. The system according to claim 13, further comprising a pair of supplementary sensors to measure a concentration of the combustible component in the flow of the gaseous feed, wherein the pair supplementary sensors comprise one supplementary sensor positioned upstream of the mixer and another supplementary sensor positioned downstream of the mixer and wherein the pair of supplementary sensors are operatively associated with the second fresh air valve and the supplementary gaseous feed valve for controlling the concentration of the combustible component in the flow of the gaseous feed leaving the mixer.

15. The system according to claim 2, further comprising a ventilation air filter for filtering coal dust from the ventilation air.

16. The system according to claim 15, wherein the ventilation air filter is positioned upstream relative to the flame arrestor.

17. A ducting system for conveying a flow of a gaseous feed of ventilation air derived from a coal mine comprising a combustible component from an inlet to at least one combustion module, the system comprising: a shut-off valve configurable to have an open position to allow the flow of the gaseous feed from the inlet to the at least one combustion module and a closed position to prevent the flow of the gaseous feed from the inlet to the at least one combustion module; a sensor to measure a concentration of the combustible component in the flow of the gaseous feed, the sensor located upstream of the shut-off valve; a flame detector located downstream of the shut-off valve; a flame arrestor located in a flow path of the gaseous feed upstream of the shut-off valve; a source of fire retardant and a fire retardant valve feeding one or more fire retardant injection points for controlling flow of the fire retardant into the ducting system, the one or more fire retardant injection points positioned between the flame arrestor and the at least one combustion module; a supplementary gaseous feed in fluid communication with a gas mixer for mixing the gaseous feed with the supplementary gaseous feed, the supplementary gaseous feed comprising a supplementary combustible component; a supplementary gaseous feed valve for controlling flow of supplementary gaseous feed into the flow of the gaseous feed downstream of the shut-off valve; a source of fresh air and a fresh air valve for controlling flow of the source of fresh air into the flow of the gaseous feed at a position upstream of the mixer; and a pair of supplementary sensors to measure a concentration of the combustible component in the flow of the gaseous feed, wherein the pair of supplementary sensors comprise one supplementary sensor positioned upstream of the mixer and another supplementary sensor positioned downstream of the mixer, wherein the shut-off valve is operatively associated with the sensor such that a measurement of a concentration of the combustible component in flow of the gaseous feed over a specified concentration by the sensor causes the shut-off valve to be configured to the closed position for preventing flow of a gaseous feed comprising a combustible mixture of the combustible component from reaching an ignition source, wherein the specified concentration is 1.25% methane as the combustible component, wherein the shut-off valve is operatively associated with the flame detector such that detection of flame by the flame detector causes the shut-off valve to be configured to the closed position for attenuating propagation of a flame toward the inlet, wherein the fire retardant valve is operatively associated with the flame detector such that detection of flame by the flame detector causes the fire retardant valve to open allowing the fire retardant to flow into the ducting system for attenuating the detected flame, and wherein the pair of supplementary sensors are operatively associated with the second fresh air valve and the supplementary gaseous feed valve for controlling the concentration of the combustible component in the flow of the gaseous feed leaving the mixer.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic diagram of a first configuration of a ducting system according to the invention;

(3) FIG. 2 is a schematic diagram of a second configuration of a ducting system according to the invention;

(4) FIG. 3 is a schematic diagram of a third configuration of a ducting system according to the invention;

(5) FIG. 4 is a schematic diagram of a fourth configuration of a ducting system according to the invention;

(6) FIG. 5 is a schematic diagram of a crimped metal ribbon flame arrestor;

(7) FIG. 6 is a side view of a channel of the flame arrestor of FIG. 5; and

(8) FIG. 7 is a body portion ventilation air methane (VAM) combustion module.

DESCRIPTION OF EMBODIMENTS

(9) Referring initially to FIGS. 1 to 4, where like features have been given like numbers, there is provided a number of configurations of a ducting system 100 for conveying flow of a gaseous feed 110 such as coal mine ventilation air having a combustible component in the form of methane. The ducting system 100 allows a flow of gaseous feed 110 from an inlet (not shown) to a plurality of combustion modules 12.

(10) As used herein, upstream refers to a position situated in the opposite direction to the direction of flow of the gaseous feed (i.e. towards the inlet) and downstream refers to a position situated in the same direction as the direction of flow of the gaseous feed (i.e. towards the combustion modules 12).

(11) In each configuration, the ventilation air 110 flows from the inlet (not shown), through the ventilation air shaft 1 and past a sensor C0 for measuring a concentration of methane in the ventilation air. A shut-off valve 6 is operatively associated with the sensor C0 such that a measurement of methane above a specified concentration by the sensor C0 causes the shut-off valve 6 to be configured to a closed position preventing further flow of the gaseous feed 110 toward potential ignition sources such as the combustion modules 12.

(12) As shown in FIGS. 1 to 4, the sensor C0 is positioned upstream of the shut-off valve 6. It is preferred that the first sensor C0 is positioned as far underground as possible, i.e. as close to the source of the ventilation air as possible. By locating the first sensor C0 as far from the shut-off valve 6 as possible, the earlier a pocket of gas containing a potentially combustible concentration of methane entering the system 100 can be detected and preventative measures such as closing shut-off valve 6 and shutting down the combustion units 12 can be implemented.

(13) A pair of supplementary sensors C1 and C2 for measuring the concentration of methane in the flow of the ventilation air are also provided. In addition to monitoring for potentially combustible concentrations of methane, which also triggers the closure of shut-off valve 6 and shut down of the combustion modules 12 as described in relation to the sensor C0 above, the supplementary sensors C1 and C2 assist in maintaining the concentration of methane in preferred operational limits for mitigation by the combustion units 12.

(14) The supplementary sensors C1 and C2 are positioned upstream and downstream, respectively, of a mixer 8. A supplementary gaseous feed 140 comprising methane is provided in fluid communication with the mixer 8. The supplementary sensors C1 and C2 are operatively associated with a fresh air valve 7 and a supplementary gaseous feed valve 13 for controlling the concentration of the methane in the flow of the ventilation air leaving the mixer 8.

(15) The combination of the sensors C0, C1, C2 and the shut off valve 6 aim to prevent fire occurring by maintaining the concentration of methane below its lower explosive limit and, where a measurement of the concentration of methane above a specified value is detected, preventing flow of the ventilation air comprising a potentially combustible mixture of methane from flowing towards potential ignition sources such as the combustion modules 12. However, in the event that the preventative measures should fail, the ducting system 100 is further provided with measures, as described below, for attenuating a flame should ignition of the ventilation air occur.

(16) Flame detectors F0, F1, F2, F3, . . . , Fn are provided downstream of the shut-off valve 6. The flame detectors F0, F1, F2, F3, . . . , Fn are shown positioned adjacent each combustion unit 12, however it will be appreciated that additional flame detectors F0, F1, F2, F3, . . . , Fn may be positioned adjacent any ancillary equipment that may present as a potential ignition source. The shut-off valve 6 is operatively associated with the flame detectors F0, F1, F2, F3, . . . , Fn such that detection of a flame by any one of the flame detectors F0, F1, F2, F3, . . . , Fn to be configured to a closed position thereby providing a barrier to the flame from propagating toward the inlet.

(17) A source of fire retardant 11 and a fire retardant valve 10 for controlling the flow of fire retardant into the system may also be provided. The fire retardant valve 10 is operatively associated with the flame detectors F0, F1, F2, F3, . . . , Fn such that detection of flame by the flame detector F0, F1, F2, F3, . . . , Fn causes the fire retardant valve 10 to open allowing fire retardant to flow into the ducting system at one or more fire retardant injection points defining a fire injection zone for attenuating the detected flame. For example, the fire retardant is configured to flow into the system at fire retardant injection points on both sides of the shut-off valve 6 such that, as the detection of the flame by the flame detectors F0, F1, F2, F3, . . . , Fn causes the shut-off valve 6 to close, the fire retardant would be prevented from flowing to sections on either side of the shut-off valve 6. Furthermore, the fire retardant is preferably configured to flow into the ducting system 100 at fire retardant injection points upstream of potential ignition sources to provide additional time from the detection of a flame for the fire retardant to flow into the ducting system 100.

(18) Burst panels 23 are further provided between the fire retardant injection points and the combustion modules for releasing the pressure inside the ducting in the event of fire or an explosion. In the event of a flame detection by the flame detectors F0, F1, F2, F3, . . . , Fn, shut-off valve 6 closes and fire retardant valve 10 opens allowing fire retardant to flow into the ducting system downstream of the shut-off valve. The introduction of fire retardant and closure of the shut-off valve may lead to an increase in pressure in the portion of the ducting downstream of the shut-off valve. This increase in pressure may be as a result of the flame propagation, the introduction of pressurised fire retardant and the reaction between the flame and the fire retardant (e.g. heating of a gas fire retardant or vapourisation of a liquid fire retardant such as water). This increase in pressure leads to a bursting of the burst panels 23 which protects this portion of the duct from deformation and provides a low pressure path for the flame to be directed outside of the ducting system 100.

(19) A flame arrestor 5, described in more detail below, is further provided upstream of any potential ignition sources including the shut-off valve 6. Any flame that progresses through the above described flame attenuation measures comes into contact with the flame arrestor for further attenuation. It will be appreciated that, in the event that the above measures fail to quench the flame entirely, the flame will be greatly attenuated relative to a system not including such measures.

(20) As the combustion modules 12 present a potential ignition source, additional flame arrestors may be provided in close proximity to the combustion modules 12, for example between the combustion module 12 and the combustion module inlet valve 22. Positioning a flame arrestor close to an ignition source can minimise the potential distance of travel of a flame originating at the combustion module 12 which decreases the likelihood of the flame undergoing a deflagration to detonation transition (DDT). As such, any flame arrestor positioned between the combustion module 12 and the combustion module inlet valve 22 may be a deflagration rated flame arrestor. The presence of a flame arrestor in proximity to the combustion modules may also reduce the physical requirements of the flame arrestor 5 positioned upstream of the shut-off valve 6.

(21) Specific configurations of the ducting system 100 will now be described with reference to FIGS. 1 to 4.

(22) Configuration 1

(23) Referring to FIG. 1, a fully enclosed ducting system 100 is provided comprising a ventilation air fan 2 for conveying the flow of coal mine ventilation air 110 containing the combustible component methane from the ventilation air shaft 1 through a main duct 120 to a plurality of ventilation air methane (VAM) combustion modules 12, where each VAM combustion module 12 is fluidly connected to the main duct via a respective combustion module pipe 130.

(24) From the ventilation air shaft 1, the coal mine ventilation air 110 passes through a ventilation air filter 4 for filtering coal dust from the ventilation air and a flame arrestor 5. The flame arrestor 5 may be any suitable flame arrestor, for example a crimped metal ribbon flame arrestor 300 of the type shown in FIGS. 5 and 6 and as discussed in more detail below. By locating the flame arrestor 5 in a flow path of the coal mine ventilation air 110, this may attenuate propagation of a flame between the combustion module 12 and the inlet. This may be advantageous should other fire prevention measures fail and ignition of the coal mine ventilation air 110 in the system 100 were to occur.

(25) A three-way butterfly valve 6 is provided such that, when operated, simultaneously stops the flow of ventilation air 110 toward the VAM combustion modules 12 and opens a valve to allow a flow of fresh air into the system thereby to dilute the concentration of methane in the flow of the ventilation air 110. The three-way butterfly valve 6 is operated in the event of the detection of a concentration of methane above a specified value by any one of the methane sensors C0, C1, C2 located throughout the ducting system, or the detection of flame by any one of the number of flame detectors F0, F1, F2, F3, . . . , Fn. The three-way butterfly valve 6 may be automatically operated after receiving a control signal from a controller (not shown), which may provide the control signal in response to sensor signals from methane sensors C0, C1, C2 and flame detectors F0, F1, F2, F3, . . . , Fn.

(26) An additional fresh air supply is provided, with the flow of fresh air into the flow of ventilation air controlled by fresh air valve 7. During standard operation, when the methane concentration is required to be brought down by operational requirements of the downstream VAM combustion modules 12, the fresh air is sucked into the ventilation air by controlling the fresh air valve 7. The fresh air flow rate is controlled by the methane sensors C1 and C2. C1 is used to monitor the methane concentration in the ventilation air, and C2 for the methane concentration after the valve 7, i.e. the methane concentration in the flow of ventilation air 110 being conveyed to the VAM combustion modules 12.

(27) When the methane concentration is required to be brought up to a certain level for the self-sustaining operation of the downstream VAM combustion modules, a supplementary gaseous feed 140 such as coal mine drainage gas is injected into the flow of ventilation air 110 through mixer 8. The supplementary gaseous feed 140 is supplied from a source through a supplementary gaseous feed pipe 150 comprising a supplementary gaseous feed valve 13, fuel filter 14, fuel flame arrestor 15, fuel check valve 16, fuel pressure regulator 17 and fuel valves 18. The flow rate of the supplementary gaseous feed 140 is monitored and controlled via a fuel flow monitor and controller 19. The supplementary gaseous feed 140 flow rate is determined by methane sensors C1 and C2. C1 is used to monitor the methane concentration in the flow of ventilation air upstream of mixer 8, and C2 for the methane concentration downstream of mixer 8, i.e. the methane concentration in the flow of ventilation air 110 being conveyed to the VAM combustion modules. The mixer 8 can be any type of mixer for mixing the supplementary gaseous feed 140 and flow of ventilation air 110, e.g. an array of fuel nozzles around the ventilation air ducting.

(28) In the event of a methane reading by any one of the methane sensors C0, C1, C2 above the specified value, for example a value of 1.25%, the valve 6 will be operated to be closed to the flow of ventilation air 110 and open to the fresh air supply. In addition, the two fuel valves 18 will also be operated to close to ensure no additional methane is being introduced to the system, and the VAM combustion modules 12 are shut down. Valves 6, 18 and the VAM combustion modules 12 will be similarly operated in the event of any one of the flame detectors F0, F1, F2, F3, . . . , Fn detecting a flame.

(29) In addition to the flame prevention measures discussed above, the ducting system also provides a number of measures for suppressing flame propagation should fire occur. One measure includes the provision of a flame arrestor 5, discussed in more detail below, in the flow path from the ventilation shaft 1 to the VAM combustion modules and an additional flame arrestor 15 in the supplementary gaseous feed pipe 150. In addition, a source of inert gas 11, for example compressed CO.sub.2, is also provided with flow of CO.sub.2 into the ducting system 100 controlled by inert gas valve 11. The inert gas valve 11 is configured to open in the event of a flame being detected by any one of the flame detectors F0, F1, F2, F3, . . . , Fn such that CO.sub.2 flows into the main duct at various positions through an array of nozzles.

(30) To avoid ventilation air fan 2 back pressure and shaft exit blockage when the ducting system is not operated correctly or in the case of emergency where the three-way butterfly valve 6 is closed to the flow of ventilation air 110, two gravity-based hanging doors 3 (one per side) can be used. The hanging doors 3 can be pushed open automatically by ventilation air pressure. When the ducting is in normal operation, and a pressure balance is achieved by the extraction fan 9, the hanging doors 3 are in a closed position. The selection of the cross-sectional area of the hanging doors 3 is dependent on the ventilation air flow rate and pressure.

(31) One or more burst panels 23 are installed downstream of the mixer 8 to release the pressure inside the ducting if the explosion occurs. The burst panels 23 can be rated to 50 kPa or 100 kPa or other valve, and the use of burst panels 23 can reduce the required duct wall thickness. The size of the burst panels 23 is determined based on the duct size and gas flow rate in the duct.

(32) A drainage valve 21 is also provided for draining any condensed water inside the ducting.

(33) Configuration 2

(34) A second configuration of a ducting system is shown in FIG. 2. Configuration 2 is a similar set up to configuration 1 however some of the components of the ducting system of FIG. 1 are provided in each individual combustion module pipe 130 leading to the VAM combustion modules 12. In this way, if there is a high methane reading at sensors C0, C1, C2 in one of the combustion module pipes 130, or flame detected at flame detector F1 in one of the combustion module pipes, only the affected pipe will be shut down and the remaining VAM combustion modules 12 on unaffected pipes can continue to operate. This configuration also allows flexibility in whether some or all the VAM combustion modules 12 are provided with fuel mixing to control the methane concentration. Furthermore, with a ducting system 100 of this configuration, the maintenance, replacement or other work being conducted on components of the ducting system may only require the VAM combustion module 12 on the affected combustion module pipe to be shut down, allowing the other VAM combustion modules on the remaining combustion module pipes to continue to operate.

(35) Configuration 3

(36) Configuration 3 is the same as configuration 1 applied to an unenclosed ducting system 100 whereby a ventilation air hood 20 is used to collect ventilation air 110 from above a ventilation air shaft outlet 160.

(37) Configuration 4

(38) Configuration 4 is the same as configuration 2 applied to an unenclosed ducting system 100 whereby a ventilation air hood 20 is used to collect ventilation air 110 from above a ventilation air shaft outlet 160.

(39) Flame Arrestors

(40) Flame arrestors are designed to allow the flow of gas therethrough while preventing the propagation of a flame front by removal of heat from the flame as it passes through the flame arrestor. In general, there are two important regimes of explosion: deflagration and detonation. Deflagration normally propagates at a velocity below the speed of sound and the maximum pressure is 0.7 MPa. Detonation waves proceed at supersonic velocities, ranging from 1,000 m/s to 2,500 m/s with a maximum pressure up to 1.7 MPa and can cause extreme destruction that is much harder to arrest than deflagration. It is therefore very important to determine whether and how deflagration or detonation can occur for various geometries and mixture compositions of ventilation air ducting so that optimum safety requirements can be designed into the ventilation air ducting system.

(41) In the above described ducting systems, flame arrestors 5 are positioned between the combustion modules 12 and the ventilation air shaft 1 to suppress the flame propagation back to the mine in the event that ignition of the flow of gaseous feed were to occur. Additional flame arrestors 15 are provided in the supplementary gaseous feed pipe. It will be appreciated that further flame arrestors may also be provided adjacent potential ignition sources to at least partially quench a flame should ignition occur and therefore reduce the load on the final flame arrestor 5. For example, combustion module flame arrestors may be positioned proximal to the combustion modules 12. Selection of a flame arrestor rated for deflagration and/or detonation depend on how the ducting is designed for its practical application, such as its length, diameter, shape, bends and equipment. It is important to design the ducting in a manner to minimise the likelihood of a deflagration to detonation transition (DDT) should a fire occur, for example by minimising features in the ducting that could increase turbulence of a flame, such as elbows, sensors and other attachments.

(42) There are many types of flame arrestors. A flame arrestor for use in the safe ducting system may comprise crimped metal ribbon, parallel plate, expanded metal cartridge, perforated plate, wire gauze, sintered metal, metal shot, ceramic balls and/or compressed wire wool flame arrestor elements.

(43) Referring to FIGS. 5 and 6, crimped metal ribbon flame arrestor elements 200 are characterised by alternating layers of crimped metal ribbons 210 and flat metal ribbons 220 which are wound together to form a layered cylinder. The spaces between the crimped and flat ribbons provide multiple small channels 230 of approximately triangular cross-section.

(44) Crimped metal ribbon flame arrestor elements can be characterised by a number of parameters, including ribbon thickness, element thickness b and element diameter D. The channels formed in the spaces between the corrugations and the flat ribbon can be characterised by the height h and bottom side width a of the triangle, as shown in FIG. 6. The path length L is defined by the element inclination a and the element thickness b, i.e. L=b/a. The expansion ratio is defined as the ratio of the element diameter D to the pipe diameter d, i.e. =D/d.

(45) The design of a crimped metal ribbon flame arrestor element suitable for use in ducting between a coal mine ventilation air shaft and VAM combustion modules must take into account various features specific to the system such as flow rate of the ventilation air through the ducting, composition, dust content and pipe size.

(46) For example, it has been found that channels of smaller cross-sectional area increases flame quenching efficiency, however smaller channels are more prone to fouling with coal dust which can lead to increased requirement for cleaning and replacement of the arrestor, potential failure of quenching and increased ventilation air flow resistance. Similarly, increased channel length L has been found to increase flame quenching efficiency, while also increasing the flow resistance. The crimped metal ribbon flame arrestor path length L may be of any suitable length, preferably from about 10 mm to about 250 mm. It will be appreciated that the path length for a system can be increased by providing two or more crimped metal ribbon arrestor elements in series.

(47) The expansion ratio (3, the ratio of the element diameter D to pipe diameter d, can also be an important parameter. It has been found that increasing the expansion ratio, i.e. increasing the element diameter D increases the flame quenching efficiency. However, pipes used in conveying coal mine ventilation air are significantly larger than pipes for which flame arrestors are currently designed for. For example, the main duct 110 for conveying coal mine ventilation air 110 may be in the order of about 5 m in diameter. Combustion module pipes are generally significantly smaller in diameter than the main duct, for example the combustion module pipes may be around 1 m in diameter.

(48) Preferably, the flame arrestor has an expansion ratio greater than about 1, preferably from about 1 to about 5, and more preferably about 2. However, increasing the element diameter D can lead to increased risk of damage during handling, installation and use with the potential for enlarged or collapsed channels which can decrease the flame quenching efficiency and increase flow resistance. To increase durability, support members may be introduced to the flame arrestor, such as metal rods, extending radially through the cylinder of the flame arrestor. Furthermore, two or more crimped metal ribbon flame arrestor elements can be provided in parallel to provide process higher ventilation air flow rates without needing to increase the diameter of the flame arrestor elements.

(49) VAM Combustion Modules

(50) Suitable VAM combustion modules include the system for mitigating a volatile component from a gaseous feed as described in AU 2009338680 and the system for catalytic combustion as described in U.S. Pat. No. 7,430,869, both of which are incorporated herein by reference.

(51) In certain embodiments, VAM mitigation combustion modules 12 of the type described in AU 2009338680, which is incorporated herein by reference, are used. Referring to FIG. 7, the body portion 300 of the VAM mitigation combustion module 12 includes an array of bores 310 that extend through the body portion 300 from a first end to an opposing second end. The bores 310 have a circular cross section with a diameter of 3 mm and are spaced apart at distance of approximately 4 mm taken from the centre points of the bores. The body portion is substantially cube-shaped, having a height, width and depth each of from about 1 m to about 3 m.

(52) During start-up of the combustion module, the body portion is heated to a desired temperature, generally about 1200 C. Inclusion of a catalyst in the body portion, for example within the material of the body portion itself or applied to the walls of the bores extending therethrough, may dictate a relatively low start up temperature of from about 200 C. to about 700 C.

(53) The ventilation air containing methane flows through the bores of the body portion. The ventilation air is initially at a temperature of about 25 C. (i.e. ambient temperature) and increases in temperature as it passes through the combustion module by absorbing heat from the inner walls of the bores until it reaches auto-ignition temperature of the methane. At this point, oxidation takes place resulting in relatively high temperature gaseous emission that provides heat to the body portion as it exits the combustion module. The direction of ventilation air flow through the body portion may be periodically reversed between a forward flow 320 and a reverse flow 330 to utilise the heat generated by the combustion process and therefore reduce the energy consumption of the combustion module 12.

(54) In other embodiments, VAM catalytic combustion modules 12 of the type described in U.S. Pat. No. 7,430,869, which is incorporated herein by reference, may be used. VAM catalytic combustion modules 12 may include a body portion in the form of a honeycomb-type monolith catalytic combustor. The catalytic combustor may contain any suitable catalyst for the system, for example a catalyst having an activity of 5010.sup.7 to 20010.sup.7 mole/m.sup.2s and a reaction surface area of 20 to 40 m.sup.2/cm.sup.2. The honeycomb-type monolith catalytic combustor may comprise a ceramic monolith which acts as a substrate for a wash coat slurry of base metals on which a noble metal catalyst is placed.

(55) It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.