Mining or in situ disintegration of hard material – Processes – Mine safety
Patent
1996-04-01
1998-10-13
Bagnell, David J.
Mining or in situ disintegration of hard material
Processes
Mine safety
299 67, F21F 500
Patent
active
058202234
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to highwall mining of a seam of aggregate material.
In particular, the present invention relates to a highwall mining system of the type which comprises: form a drive in the seam, drive; and circulating the atmosphere at least at the forward end of the drive.
The highwall mining system of the present invention is suitable particularly, although by no means exclusively, for mining coal from a seam extending from an exposed face in a high wall of an open cut mine.
Highwall mining of coal offers the potential for low cost recovery of coal that cannot normally be recovered economically by conventional surface or underground mining operations.
One of the areas of concern for highwall mining of coal, especially as the penetration depth of drives increases, is the possibility of explosions resulting from methane and/or other gases seeping into drives and/or coal dust generated in the process of mining coal.
Explosions have occurred in U.S. highwall mining operations, resulting in injuries, and thus there is considerable incentive to develop a highwall mining system which can avoid explosions.
The explosive limits for methane in air are in the range of 5 to 15%. As the oxygen concentration in the gas mixture decreases (from 21% present in air), the explosive range of methane concentrations reduces and at an oxygen concentration below 12.2% (at ambient temperatures) an explosion with methane cannot occur.
Conventional underground mining operations require that ventilation be provided to dilute and exhaust explosive gases and that methane levels be monitored. Specifically, in conventional underground mining operations, if methane levels reach 1.25% an alarm sounds and all power is shut off and if methane levels reach 2.5% the mine must be evacuated. However, in a highwall mining operation, where ventilation of a drive is not required, methane concentrations could reach or exceed explosive limits in air without difficulty.
There is only very limited publicly available information on the explosive limits of hybrid mixtures containing methane and coal dust in air or in atmospheres with oxygen concentrations less than 21%. Nevertheless, on the basis of research work carried out for the applicant it appears that at oxygen concentrations below 9% an explosion with hybrid mixtures containing methane and coal dust can not occur. This research work was conducted using coal samples representing one Queensland mine where highwall mining is proposed. Similar work is needed to confirm the result for coal types found in other mines.
An object of the present invention is to provide a highwall mining system of the type described above in sub-paragraphs (a) and (b) which avoids explosions caused by ignition of methane gas and/or coal dust and/or other flammable materials in a drive.
According to the present invention there is provided a highwall mining system for mining aggregate material from a seam comprising: forming a drive in the seam; drive; circulating the atmosphere at least at the forward end of the drive; and the atmosphere in the drive lower than the concentration of oxygen required for explosion of methane gas and/or dusts and/or other flammable materials in the drive, the inertization means comprising: into the drive, the inertization gas injection means having an outlet for inertization gas located during the early stages of forming the drive on or in the region of the mining means and, thereafter, on or in the region of the mining means and/or at the entrance of the drive and/or between the entrance of the drive and the mining means; and
The present invention is the consequence of experimental work carried out by the applicant which showed unexpectedly that, in the absence of an effective barrier to restrict gas flow into and from a drive, a stratified gas recirculation flow is set up by a circulation fan of a continuous miner which has the effect of inducing external air flow into the drive along the bottom of the drive and exhausting gas flow from the drive along the top of the drive.
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REFERENCES:
patent: 3922015 (1975-11-01), Poundstone
patent: 4465155 (1984-08-01), Collins
patent: 5253925 (1993-10-01), Modzik, Jr.
patent: 5261729 (1993-11-01), Addington et al.
patent: 5273344 (1993-12-01), Volkwein et al.
Marshall Gordon Alexander
Rigby Geoffrey Raymond
Bagnell David J.
The Broken Hill Proprietary Company Limited
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