AU2008200753A1 - Inert Gas Generator - Google Patents

Description

00 Inert Gas Generator Field of the Invention S The invention relates to inert gas generators for mining and other applications.

Background of the Invention 0Mining is an inherently dangerous activity. Coal mining is particularly dangerous because of the risks associated with ignition of the combustible gases produced from the extraction of coal.

Coal is formed by tons of pressure being exerted upon carboniferous debris which has been buried. Over periods of several millions of years the debris is converted into coal. Coal, a fossil fuel, is desirable as an energy source as it is combustible when heated. Coal is extracted from its subterranean location by miners who in modern times operate large and cumbersome automated metal machinery.

During the process of coal extraction, methane gas from coal deposits leaches into those parts of the mine workings from which coal has been extracted. The presence of methane in and about the area from which coal is being or has been extracted combined with the use of metal extraction tools is extremely dangerous to the miners operating the mining equipment as methane gas is highly combustible. The presence of large quantities of combustible gases, namely, oxygen and methane along with coal dust in the mining area means that there is a substantial risk of ignition and explosion of the gases arising from an ignition source in the mine or spontaneous combustion of the gases or coal where heat emanating from the machinery operation or burning coal reaches a critical ignition temperature. There is a high likelihood that such an explosion could kill miners working in the immediate area and may also lead to the collapse of the walls and ceilings of nearby already mined areas thereby putting at risk the lives of mining personnel engaged at other locations in the mine. The costs and adverse impacts of loss of life are high indeed.

00 In addition, in the case of mine collapse, there is a substantial cost associated with the loss of or damage to mining equipment. The typical costs of replacing such equipment are significant and may run into millions of Sdollars (depending upon the type of equipment).

t 5 In order to enhance the safety of the mine workers and to reduce the exposure of mine operators to financial risks it is desirable to reduce the c likelihood of combustion of the atmospheric gases generated in coal and other t mineral extraction occurring.

It is an established practice by those skilled in the art to pump inert gas (Ni 00 10 into a mining or mined area to reduce the risk of explosion of combustible gasses in the presence of sufficient quantities of oxygen. The inert gas acts as a gaseous envelope, purging oxygen from the mining area where ignition is possible. Nitrogen and carbon dioxide are inert gases, being non-combustible.

Combustible gases such as methane when combined with the oxygen found in the atmosphere at mining extraction zones present a danger of explosion.

Inert gas generators are used in coal mining operations to reduce the risks of explosion of combustible gases, particularly methane, which has an ignition temperature of 390 degrees Celsius, which is within the range of temperatures at which mining machinery operates. It is known that the percentage by volume of the inert gases nitrogen and carbon dioxide in a given area increases when existing atmospheric gases are chemically converted through an exothermic chemical reaction produced when hydrocarbons are burnt. The temperature increase which results from the exothermic chemical reaction of mixing a hydrocarbon with oxygen creates a gaseous chemical product comprised of C02, H20 and other gases.

combustion Atmospheric air hydrocarbon C02 H20 N2 02 heat (thermal energy) Carbon dioxide is heavier than oxygen and methane in gaseous form and so, if the gaseous product of the above reaction is pumped into mine extraction regions the lighter gases, oxygen and methane, will be prevented 00 from combining into a combustible mix. The extraction zone will be

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O"blanketed" with a non-combustible gaseous envelope.

However, the heated atmospheric gases that are the by-product of the combustion of oxygen and hydrocarbons must be cooled in order to ensure V 5 that the working environment remains safe. This cooling is performed in existing IGG's by pumping large quantities of water or other cooling liquid, such as glycol, around the body of the inert gas generator. The exhaust product is thus cooled between production and delivery to the extraction zone.

0 Water at mine sites may be scarce or the supply may be unsuitable for use as a

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00oo 10 coolant as a result of the presence of chemical or toxic residues in the water 0 0 supply which may corrode machinery components. Due to the nature of the cooling mechanism employed in water-cooled IGG's, there is a substantial risk that the tubing and pipes used to transport cooling fluids around the IGG may leak or rupture thereby expelling boiling liquid. This poses a safety risk as well as the additional hazard that equipment may be damaged by the corrosive or erosive nature of the cooling liquids.

Further, water cooled IGG's require air compressors to operate effectively and require additional complicated monitoring mechanisms in order to operate at optimal levels. It would be desirable therefore to provide for an inert gas generator which employed a means other than water or liquid coolant to cool the atmospheric gases which are the by-product of the inert gas generator's combustion function.

It would also be advantageous to provide an IGG which was more easily transportable than existing IGGs which are typically very heavy and cumbersome.

Further advantage arises in providing an IGG which produces cooled inert gasses more efficiently than existing IGGs.

Objects and Summary of the Invention The preferred but inessential objects of the present invention are to provide an inert gas generator which: reduces the risk of spontaneous combustion or ignition of atmospheric gases released during mineral extraction.

00 is cost effective to produce and manufacture.

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is transportable.

is air cooled.

is capable of efficiently producing and delivering inert gas to a location t 5 at a desired temperature and pressure.

is of reduced size with respect to those inert gas generators available on the market for mining applications.

Is scalable and adaptable according to the needs of the user.

00 10 Accordingly there is provided an inert gas generator which produces non- Scombustible gases from a hydrocarbon fuel source comprising a sealed combustion system having an input valve and an output valve; a sealed aircooling system having an input valve and an output valve; a compression fan powered by a motor which feeds both the combustion and the air-cooling systems with atmospheric air at a desired pressure.

Preferably, the IGG includes a means of regulating the air pressure and hydrocarbon fuel flow through the generator.

Preferably, said combustion system includes a hydrocarbon fuel source, an ignition means, a fuel regulating means and a combustion chamber.

Preferably, the combustion system feeds heated gas from the combustion chamber through a reversing chamber which is lined with thermally resistant tiles.

Preferably, the heated gas that passes through the reversing chamber is then passed through a matrix of elongated tubes in order to maximise the dispersion of thermal energy from the heated gas and thereby to produce aircooled non-combustible gasses.

Preferably, the combustion system includes a sealed shell and tube heat exchanger for cooling the gaseous product produced by the system.

Preferably, the gaseous product of the generator is expelled through the output valve of the combustion system at a desired pressure and temperature.

Preferably, the air-cooling system includes a set of helical flights affixed to the external surface of the combustion chamber which assist in cooling the heated gas which passes through the combustion chamber.

00 Preferably, the air-cooling system includes a set of vertically offset 0 0 baffles for disturbing the flow of air through the cooling system.

Preferably, the generator is contained or mounted within an external enclosure, frame or housing.

t 5 In especially preferred embodiments, the external enclosure, frame or housing incorporates at least one eyelet to facilitate transportation of the generator.

Preferably, the generator is mounted upon a skid to facilitate 0 transportation of the generator.

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00 10 Preferably, the external enclosure, frame or housing incorporates 0 insulating panels which assist in reducing the sound emanating from the generator, protecting the generator from the weather and are aesthetically appealing.

Preferably, the external enclosure, frame or housing incorporates at least one access cover which when opened enables the removal of dust from at least one dust removal bay.

Preferably, the means of regulating the air pressure and hydrocarbon fuel flow through the generator includes an override or shut-down mechanism to ensure that the combustion and air-cooling systems are unable to function independently of the other thereby reducing the risk of overheating of the generator or the production of un-cooled gas.

In especially preferred embodiments, the generator is comprised of an integrated combustion and air-cooling system capable of delivering a gaseous product to a site at a desired temperature and pressure.

Brief Description of the Drawings/Figures Figure 1 is a diagram of two stages in the operation of the integrated sealed air-cooling and combustion systems of an inert gas generator according to a preferred embodiment of the invention; Figure 2 is a graphical perspective representation of the IGG of Fig 1 with components of the motor removed and with the aircooling flow indicated.

00 Figure 3 is a view of the IGG of Fig 2 from the rear end.

Fig 4 is a left side view of the IGG of Fig 2.

Fig 5 is a front view of the IGG of Fig 2.

C4 Fig 6 is a rear perspective view of the IGG of Fig 2.

t 5 Fig 7 is a left side view of the IGG showing external cladding and front and rear doors in situ.

SFig 8 is a rear perspective top view of the IGG of Fig 2.

Fig 9 is a right side perspective view of the IGG of Fig 2 showing Cinternal detail of the combustion chamber cooling duct.

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00 10 Fig 10 is a schematic diagram of a preferred IGG of the invention.

(Ni Best Mode and Other Embodiments of the Invention The primary aim of using an inert gas generator in mining applications is to create an envelope of inert gas around the drilling/extraction machines so as to reduce the risk of ignition of combustible gases. Inert gas generators are used to maintain a lower explosion limit (or "LEL") which is the minimum amount of oxygen required to obtain ignition or combustion to sustain a burning process. It is generally recognised amongst persons skilled in the art that an acceptable LEL comprises 5.55% oxygen which will effectively reduce the risk of dangerous combustion of atmospheric gases occurring. The inert gas generator the subject of the present invention assists in maintaining an atmosphere that comprises between 3% to 3.5% oxygen, 12 to 13% carbon dioxide, less than 100oo parts per million of carbon monoxide and around 80% nitrogen.

One of the most dangerous aspects of coal mining operations is the threat of combustion of atmospheric gasses as a result of excessive heat produced by the mining process. Similarly, heat produced during the production of inert gasses poses a substantial risk and it is necessary to cool the gasses produced by the IGG prior to transporting them to the mine working site. This cooling is achieved in the IGG of the present invention through a novel air cooling system.

The IGG of the present invention is lightweight and transportable and includes a light weight skid 1 upon which the device is mounted. The IGG is preferably contained or mounted within an external enclosure, frame or 00 housing 2. In the preferred embodiment of the invention the size and dimensions of the skid are such that it is able to be fitted on a 2.4 metre wide 9 standard flat bed tilt truck. In alternative embodiments the device may be Scustom fitted to the tray of a truck to facilitate ease of transportation between tV 5 mining locations.

The skid and/or external enclosure, frame or housing incorporates at Sleast a pair of eyelets (not shown) located respectively at the front and rear ends of the skid which may be used to secure towing lines or double lifting 0lines for cranes. Additional eyelets may be added as desired to facilitate the

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00 10 easy movement and transportation of the device in accordance with user 0requirements.

A tank 5 for the storage of hydrocarbon fuel, preferably diesel, is located at the lower front end of the IGG. In the preferred embodiment the tank 5 is of such a size as to contain enough fuel for two hours operation of the IGG only. The reduced size of the tank reduces the risk of fire, decreases the overall weight of the IGG and minimises the amount of storage space required within the IGG. The tank has a level control, a monitor gauge and an inlet valve (not shown) to which may be attached an external fuel source. The valve incorporates a "Wiggins Fitting" which is a standard fitting used in the mining industry for attachment to an external fuel source.

Adjacent to the tank 5 is a fuel pump 6 which feeds a motor 3, preferably diesel, which drives a drive shaft. Any commercially available motor fit for the purpose and size of the housing of the IGG may be used. The motor 3 incorporates an air filter and a radiator which assists in cooling the motor so that it does not overheat when in operation. The driveshaft is attached to a compression fan 60 (located within a housing 18) via a step up drive train 4 which disturbs the air surrounding it and forces the disturbed air through a heat exchanger uptake duct 11 and through a set baffles 12 which are vertically offset as indicated in Figure 1. This airflow produces a cooling effect via a sealed shell and tube heat exchanger cooling system 9 which is more fully described below.

The cooling component consists of the compression fan 60 which is configured in such a manner that it achieves sufficient pressure and volume of air to provide the correct level of heat exchange through out the system. The 00 fan 60 consists of a radial tipped impeller to provide the correct balance of 0 0pressure and volume for the input power level. The fan is belt driven using a (Ni drive train 4 which includes a heavy duty timing belt, utilising a larger pitched C4 drive pulley to match the optimum running points for both the fan 60 and the f 5 diesel drive motor 3.

The disturbed air generated by the fan 60 is fed through an uptake duct C11 joined to the fan housing 18 through which atmospheric air is forced at t pressure by the fan 60 around a series of baffles 12. The baffles are joined in a perpendicular fashion to a matrix of tubes 24 through which travels the oo 10 gaseous product of the combustion system described later. The purpose of the 0baffles is to increase the turbulence and velocity of the air generated by the fan so as to maximise the energy transfer or' cooling' for the heated gases within the tube matrix 24. The combustion gas travels in the opposite direction to the fan-generated cooling air flow to maximise the energy transferred. The location of the uptake duct 11 with respect to the fan housing 18 may be modified according to the needs of the user and may incorporate a filter or have attached to it a cooler to enhance or improve the operation of the air-cooling system.

After being forced around the baffles 12, the disturbed air generated by the compressing fan 60 passes through a transition void 13 which surrounds an enclosed reversing chamber 23 which forms part of the combustion system The disturbed air is then forced at pressure through a helical flute which surrounds a combustion chamber 22 where the exothermic chemical reaction that produces inert gasses takes place, and which is enclosed within a cylindrical casing or combustion chamber cooling duct 16. The air acts to cool the gasses produced in the combustion chamber 22 before it is vented out of the IGG and into the atmosphere through a cooling-air outlet 17.

The sealed combustion system 20 produces inert gasses as a by product of the exothermic chemical reaction between atmospheric gasses and hydrocarbon fuel at high temperature. A burner 21 is located at the entrance to a cylindrical combustion chamber 22. The chemical reaction is started by a high energy ignition electrode (spark) located at the entry point of the atmospheric gasses into the combustion chamber and incorporated into the mechanism of the burner 21. A regulated quantity of hydrocarbon fuel flows 00 to the burner 21 from the fuel tank 5 by way of fuel pump 6. The atmospheric 0 0air required for the production of inert gasses is fed into the combustion system 20 via a transport duct 70 which runs off the heat exchanger uptake CT duct 11. The combustion chamber 22 and the gas produced within it is air 5 cooled by means of atmospheric air being forced through the helical flute or flights 15, described previously, which is affixed to the external surface of the c furnace chamber 22A. The combustion chamber 22 is attached to a reversing chamber 23 through which the inert gasses pass at pressure. The flights assist in cooling the heated gas which passes through the furnace chamber 22 00 10 to the reversing chamber 23 by the dissipation of heat across the surface area of the flights 15 and chamber walls 22A.

The reversing chamber 23 changes the direction of the generated inert gas as it is expelled under pressure from the combustion chamber 22. The reversing chamber 23 is lined with refractory tiles cast into the rear door which shield and insulate the metal of the reversing chamber's surface from overheating through direct contact with the heated gases which pass through it from the combustion chamber 22. The gases are redirected as they pass through the reversing chamber 23 whereupon they travel through a matrix of cylindrical tubes 24. The gases are slowed down prior to entering the tubes 24 to maximise the time taken to reach the opposite end of the sealed shell and tube heat exchanger 9. The tubes 24 serve the purpose of exposing the heated gas to the maximum possible surface area as it passes through the tube matrix so as to maximise the cooling benefits from the disturbed air generated by the compression fan 6o which circulates and surrounds the tube matrix 24.

The inert gas mixture leaves the tube matrix 24 and is passed through an exhaust plenum 25 and through an inert gas outlet 26 to which may be attached an outlet pipe, which is either rigid or flexible, for directing the inert gaseous mixture to the mine working extraction zone.

The pressure at which the compressed air is forced by the fan 6o through the cooling system is controlled by the speed at which the fan 6o is driven by the motor 3.

The volume of air delivered to the combustion system to feed the chemical combustion reaction is controlled by a butterfly valve 8 which is set within the transport duct 70 leading off the uptake duct 11. A further fuel oo00 regulating valve 7 located downstream from the butterfly valve 8 regulates the 0 0flow of hydrocarbon fuel to the burner 21 from the fuel tank 5 by way of the 9 fuel pump 6. The exothermic chemical reaction occurs within a cylindrical combustion chamber 22 where atmospheric gasses and hydrocarbons are V) 5 combined to produce inert exhaust gasses and thermal energy. The gaseous exhaust product of the reaction travels from the combustion chamber 22 C" through the sealed combustion system t The mix of atmospheric air and hydrocarbon fuel is maintained at a ratio of 99:1 which is the optimal ratio for operating the device. This ratio may oo 10 vary depending upon the hydrocarbon fuel source used however the mix is 0controlled according to a predetermined stoichiometric balance. The volume of exhaust gas produced by the IGG can be increased or decreased according to the requirements of the user by merely increasing or decreasing the speed of the compression fan 60. Accordingly, no specialist skill is required to operate the machine.

Atmospheric oxygen content is typically between 20.8% to 20.9%. The IGG of the present invention has been found to be capable of producing inert gas at a volume of 860 m 3 per hour, however greater volumes are possible with a scaled up device. The flashpoint of methane is approximately 390 degrees Celsius. The inert gas flow produced by the present invention is maintained at a temperature of between 100oo and 200 degrees Celsius which is well within safe operating temperatures.

As an additional feature to the integrated combustion and cooling systems, dust from the combustion process is drawn away from the operative parts of the systems towards the floor of the device and may be easily removed by opening access covers from dust removal bays 29 located towards the bottom portion of the sides of the device.

In the preferred embodiment of the invention, the electrical controls used to regulate the integrated combustion and air-cooling systems are an offthe-shelf product which are powered by self-contained 240 volt power source.

These may also be powered by a 24 volt DC power source. The controls enable the IGG operator to effectively monitor the fuel level, power source output and the volume of inert gas which is produced by the device. An override or shutdown switch has been incorporated into the controls which ensures that -11- 00 neither the combustion nor air cooling systems can operate without the other Calso being in operation.

N The IGG of the preferred embodiment has physical dimensions of metres length, 2.35 metres width, 2.9 metres height, 11 tonnes weight.

tV 5 However, the physical dimensions of the IGG may be readily adapted to suit specific applications. The machine is readily scaleable and the overall dimensions can be increased or decreased according to the required exhaust output and/or purpose for which the IGG is to be used. The location of the Cfeatures of the device may be changed according to design specifications

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00 10 particular to any given user's requirements and the scope of the invention Cshould not be limited in that regard.

The IGG is preferably contained or mounted within an external enclosure, frame or housing 2 and is clad externally with sound dampening foam-core insulating panels which assist to shield the mechanical operating parts from extreme weather and increase the overall aesthetic appeal of the IGG. The external aspect of the IGG incorporates front and rear roller doors 27 and 28 respectively which permit access to the motor, drive train, and other mechanical parts of the device for routine maintenance.

Those skilled in the art will appreciate that there are a variety of applications for which the present device is well suited. The device may be used in high wall mining applications including those which employ either augers or continuous mining machines. The device may also be employed to pump inert gases into coal extraction zones which are located underground at considerable depth using hoses which pump inert gas mixture down ventilation shafts to already mined goaf areas. Persons skilled in the art will recognise that the device has immediate use in relation to coal mining however it also is suitable for use to produce inert gases in other mining applications and environments where there poses a significant safety risk of explosion from the ignition of combustible gases.

Although the primary application of the present invention is in coal mining, those skilled in the art will appreciate that the device might also be employed for purging LP storage vessels prior to internal inspections, purging sewerage digesters prior to internal maintenance, purging fuel storage tanks prior to internal inspections, dilution of process gas streams to adjust calorific -12- 00 value or chemical composition. Additional compression devices may be 0 externally fitted to the device of the present invention according to user requirements.

V' 5 Advantages Amongst the advantages of the preferred embodiment of the present invention Sare:- 1. The device is scaleable depending upon the output of inert gas required oo 10 by the user. The present invention may be made to fit any sized mining 0operation without any corresponding loss of functionality. Component parts may be replaced easily with off the shelf components of various sizes.

Standard high wall mining techniques require inert gas to be generated at the rate of 18oo00 cubic metres per hour. A different sized burner may be fitted to the present invention in order to increase or decrease the gaseous output of the machine according to user requirements.

2. The present invention produces more inert gas per quantity of energy consumed than other IGGs that are currently in use in mining applications.

3. When compared to existing IGG's presently available, the IGG of the present invention: produces non-combustible gas of at least the same quality.

is more compact in size and therefore more easily transportable.

produces a greater or equal output of non-combustible gases.

may be used in parallel with existing IGG's to improve overall mining efficiency and safety.

utilises components which have a longer life span.

4. The IGG of the present invention can be modified for use in highwall mining, auger or reticulation mining application relatively easily and inexpensively.

-13- 00 5. There is no need to compress the non-combustible gas product for use 0 in auger mining applications.

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rj 6. Industry standards in the mining industry require the use of an IGG.

tn 7. Can be used for either above or below ground mining applications.

8. Can use alternative power sources.

00 10 9. Controls can be either custom fitted or not included as desired.

Claims (9)

1. 2. The generator of claim 1 which includes a means of regulating the air pressure and hydrocarbon fuel flow through the generator.
2. 3. The generator of claim 2 wherein said combustion system includes a hydrocarbon fuel source, an ignition means, a fuel regulating means and a combustion chamber.
3. 4. The generator of claim 3 wherein the combustion chamber feeds heated gas through a reversing chamber which is lined with thermally resistant tiles. The generator of claim 4 wherein the heated gas that passes through the reversing chamber is then passed through a matrix of elongated tubes in order to maximise the dispersion of thermal energy from the heated gas and thereby to produce air-cooled non-combustible gasses. 00e N6. The generator of claim 1 wherein said combustion system includes a sealed Sshell and tube heat exchanger for cooling the gaseous product produced by the system. I 7. The generator of claim 1 wherein the gaseous product of the generator is expelled through the output valve of the combustion system at a desired 0pressure and temperature.
4. 8. The generator of claim 3 wherein said air-cooling system includes a set of helical flights affixed to the external surface of the combustion chamber which assist in cooling the heated gas which passes through the combustion chamber.
5. 9. The generator of claim 1 wherein said air-cooling system includes a set of vertically offset baffles for disturbing the flow of air through the cooling system. The generator of claim 1 wherein the generator is contained or mounted within an external enclosure, frame or housing.
6. 11. The generator of claim 10 wherein said external enclosure, frame or housing incorporates at least one eyelet to facilitate transportation of the generator. 00 N12. The generator of claim 1 wherein the generator is mounted upon a skid to Sfacilitate transportation of the generator.
7. 13. The generator of claim 10 wherein the external enclosure, frame or housing e¢3 n incorporates insulating panels. 00
8. 14. The generator of claim 10 wherein the external enclosure, frame or housing incorporates at least one access cover which when opened enables the removal of dust from at least one dust removal bay. The generator of claim 2 wherein the means of regulating the air pressure and hydrocarbon fuel flow through the generator includes an override or shut-down mechanism.
9. 16. An inert gas generator having an integrated combustion and air-cooling system capable of delivering a gaseous product to a site at a desired temperature and pressure as hereinbefore described with reference to the drawings.