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Proceedings of The 7th International Mine Ventilation Congress
June 17-22, 2001, Cracow, Poland
ISBN 83-913109-1-4
Chapter 117
THE HISTORICAL VERIFICATION OF THE USAGE OF NITROGEN
IN MINE FIRES
Alois AdamusAssociate Professor, Institute of Safety Engineering
VSB-Technical University Ostrava
Ostrava-Poruba, Czech Republic
ABSTRACT
The use of nitrogen for fighting underground fires was based on the experience with the use of carbon dioxide. Many countries have used nitrogen successfully in their mining industry. For more then last 50 years, nitrogen has been used most widely in the mining industries of Czech Republic, later in France, Germany, Great Britain, Soviet Union and Bulgaria. An important role has been played by India, Poland, Slovakia, South Africa, USA, Australia, Romania and some other countries with a modern coal mining industry. The paper reviews historical information connected with the first use of nitrogen in several countries. Discussion dwells on the historical verification of the presented data.
KEYWORDS
Nitrogen, inertization, pure nitrogen, liquid nitrogen, nitrogen gas, underground fire, fighting fire, spontaneous heating, suppression of spontaneous heating, historical verification, deep mines, mining industry
847
THE HISTORICAL VERIFICATION OF THE USAGE OF NITROGEN
INTRODUCTION
Probably the earliest recorded case of inertisation of the atmosphere in a deep mine was at the Clackmannan mine, about 7 miles from Stirling in Scotland in the 1850s as described by Walker (1908) and mentioned by Morris (1987). A mixture of steam, CO2, N2 and SO2 was made by forcing air through a coke furnace with a spray of water. That inertisation continued for more than three weeks until, after a month, the fire was extinguished. Many cases of inertisation before and after 1900 are described by Morris (1987) and Walters (1997). The first occasion when pure nitrogen was used for the inertisation of an underground fire was on the 8th of August 1949. This was at the Doubrava Mine in the OKB (Ostrava-Karvina Coal Basin) in the Czech part of the Upper Silesian Coalfield. Since then many countries have used nitrogen for the fighting, suppression and prevention of underground fires. Adamus (1995) at the 7th US Mine Ventilation Symposium first published this use of inertisation of a mine atmosphere abroad. In Great Britain pure nitrogen was first used at Roslin Colliery in May 1953. The use of nitrogen for fighting underground fires has since been tried in Germany, France, the former Soviet Union States, India, Poland, Slovakia, Romania, South Africa, USA, Australia and other countries which have a modern coal industry.
THE DOUBRAVA MINE, CZECH REPUBLIC 1949
In the Czech Republic, the first time nitrogen was used for fighting a mine fire was in the Ostrava-Karvina Coal Basin after a methane explosion at the Doubrava mine. The incident occurred at a longwall face in the Hubert seam on February 12th, 1949. The explosion was followed by a fire, which was further complicated by other methane and coal dust explosions that occurred during sealing off the next day. It was necessary to seal all four of the mineshafts on the surface, two downcast and two upcast. The shafts were sealed with airtight plugs covered with clay and a layer of sand. The Czech patent method for fighting fires with nitrogen, registered in the Czech Republic by Mr. Wild from the "Moravia nitrogen plant Ostrava-Marianske hory", was used at the Doubrava mine when of Mr. Artur Kanczucky was the mine director, who chose this method for returning the mine to production. A cryogenic nitrogen generator manufactured by Linde, from the "Moravia nitrogen plant Ostrava-Marinske hory", was sited in the compressor hall of the Doubrava mine. The nitrogen plant was driven by 2.5-3.0MPa of air pressure. Nitrogen gas was intermittently injected into the mine from August 8th, 1949 to September 12th, 1950; the mine was then re-opened. The total quantity of nitrogen used during this time was 5.057 million m3 at a concentration of 99.5% of N2. Daily averages reached 16000-17000 m3 of nitrogen gas (10-11m3 min-1) with an output temperature + 9°C. The nitrogen gas was delivered to the shaft by a pipeline, with a diameter of 100 mm, and by drill rods with diameters of 100mm down the shaft to a level of 540 m.
GREAT BRITAIN
At Roslin Colliery cylinders of pure nitrogen were transported underground for fighting a spontaneous combustion in May 1953 (Clarke, 1959). The cylinders of nitrogen were discharged through the sampling pipes of the sealed fire.
Nitrogen inertisation was also used at Fernhill colliery (Vaughan-Thomas, T., 1964). On the 24th of July 1962 methane was ignited by shotfiring and set coal on fire in the North main heading. The fire spread and the decision to seal off the heading was made on the 25th of July. The nitrogen plant was transported to Fernhill Colliery by three lorries on the 9th of August 1964. By midnight of the 9th/10th August the plant was fully assembled and the first liquid nitrogen gas discharged from a British Oxygen Company Ltd. road tanker of 78,000 cu. ft capacity into the evaporators. The nitrogen plants consisted of two evaporators with normal rates of nitrogen flow of 30,000 cu.ft/hr. The nitrogen injection was started at 12.25 a.m. on the 10th of August with an oxygen percentage of 15.38 in the fire area. Within 24 hours, after 590,000 cu. ft. of nitrogen had been pumped in, the oxygen percentage had dropped to 10 and after a further 36 hours, when a total 1.87 million cu. ft of gaseous nitrogen had been evaporated, the oxygen percentage was 7.37. Due to the concentration changes of gases inside the fire area it was calculated that the volume of sealed off roadway inside the stopping was 400,000 cu. ft. disregarding leakage. The rate of nitrogen flow varied from 20,000 to 44,000 cu. ft/hr. A new two yard long sandbag stopping 95 yards back from the face of the heading was constructed between the 25th and 27th of November after unsuccessful re-opening of the fire area. Nitrogen was injected into the fire area from the 10th of August 1962 to the 9th of December 1962 with some short breaks. On the 9th of December, the nitrogen flow rate was cut to 4,000 cu.ft/hr. and continued up to the 11th of December 1962, when the flow was stopped. In supplying the nitrogen to Fernhill, the British Oxygen Company Ltd. tankers delivered 85 million cu.ft. of gaseous nitrogen.
Experience of the use of nitrogen gained at Fernhill colliery was used later on many occasions in Great Britain. On the 3rd of October 1980, nitrogen was injected into the waste of 15´s heavy-duty face at Daw Mill Colliery to control a spontaneous combustion heating. This was the first time in a British coalmine that nitrogen had been used on a longwall mechanised face for this purpose (Harris, 1981). More then 3 million m3 of nitrogen gas were injected into the underground fire area.
At Fryston colliery, North Yorkshire, nitrogen was used for fighting a spontaneous heating which occurred at a longwall face (Wastell, 1983). The spontaneous combustion was extinguished with nitrogen being injected through a 120mm borehole from surface to a depth of more than 500 m. Liquid nitrogen was transported to the site in 14,000 m3 capacity tankers and converted to gas by a diesel-fired vaporiser. Through the borehole were injected intermittently 765,180 m3 of nitrogen gas over a seven-month period with flow rates in the range 2.5-50 m3 min-1.
In the period between 1981 and 1984, nitrogen was used in British mines eleven times with flow rates of nitrogen gas in the range 3-25m3 min-1, twice for the inertisation of sealed areas, 8 times for suppression of spontaneous combustion in wastes and once for methane control on an advance-retreat panel (Jolene, 1984). Between 1980 and 1990 nitrogen has been injected in over 40 different sites, covering the country from Scotland to Warwickshire. In the financial year 1990/91 nitrogen was injected at seven collieries (Spedding, 1991). In the period 1979–1990 the total nitrogen consumption at Daw mill Colliery was 38.1 million m3 of nitrogen gas (Bains, 1991).
GERMANY
Equipment for nitrogen inertisation had been developed over a number of years and by the end of 1974 was available for use. The first large injection took place on the 6th of December 1974 at Osterfeld Colliery (Kugler, 1975). The nitrogen flow rate reached 60 m3 min-1 to guard against the danger of an explosion during salvage operations in a section of the mine in which a heating had developed. The colliery steam plant evaporated the liquid nitrogen; the total consumption of nitrogen gas after 6 days inertisation reached 154,000 m3. The next use of nitrogen inertisation was for dealing with a heating at the Schlagel colliery in August 1975. During 36 days 700,000 m3 of nitrogen gas evaporated by oil, electricity and colliery steam were injected.
In the period between 1974-1979 109.19 million m3 of nitrogen gas were consumed in 41 cases of inertisation (Both, 1981). The largest use of nitrogen in this period was at the Westfalen Colliery, where 13.0 million m3 of nitrogen were injected during 81 days. It was the first manless operation of underground inertisation in Germany. The literature (Both, 1990) introduces a listing of 104 cases of inertisation in the period 1974-1986 with total nitrogen consumption of 330 million m3. Nine of these examples of inertisation lasted for more than 1 year. The highest annual consumption of 46.414 million m3 of nitrogen was in 1978.
FRANCE
Nitrogen flushing equipment was developed at a time when the sub-level mining method employed in France required a high degree of spontaneous combustion control. Longwall sub-level caving uses expensive equipment and the loss of production caused by sealing off due to heatings could not be sustained. The first inertisation of the waste at a producing longwall face occurred on the face S5 in the second North seam at Rozelay Colliery in the Blanzy coalfield (Benech, 1977). This retreat longwall face was 95 m long with a seam section of 9 m, a 3 m face in the upper coal, was mined with a daily advance of 1.0 m. After 480 m of advance, abnormally high levels of CO were detected. Trials of nitrogen injection started on 23 rd of April 1976 and a nitrogen flow rate in the range from 40 to 150 m3h-1 was sustained. The nitrogen flushing was not completely successful, and the face had to be sealed off at the end of May 1976, but the use of the nitrogen flushing enabled the recovery of the face equipment These results seemed sufficiently encouraging for the consideration of the use of continuous injection of nitrogen into the wastes of sub-level caving faces as a systematic and preventive measure.
The second case of nitrogen flushing at Rozelay Colliery started on 13th of June 1976 in the face S 61 as a preventative measure after 25m of advance of the face. Nitrogen was injected at rates between 100 and 500m3h-1 dependant on the CO levels. Subsequently, from the 20th of September the blind ends of the main and tailgates were sealed systematically by stoppings and foam was injected behind them. The combination of nitrogen flushing and sealing off of blind ends with isofoam kept the face running. Nitrogen was injected from a fixed installation on the surface supplied by the Societe Union-Carbide and in July 1976 consisted of
2 liquid nitrogen tanks of 37,000 litres capacity, subsequently increased to 3 × 37,000 litres, and
1 atmospheric evaporator of 500m3h-1, subsequently increased to 4 × 500 m3h-1.
A methane fire on a longwall face was extinguished by nitrogen at the Sainte-Fontaine Colliery in May 1982 (Froger, 1985). Flames appeared above the support canopies in a fault zone and the mine was evacuated. A light barrier was built in the tailgate of the face and nitrogen was used to avoid the risk of an explosion during sealing. The flow rate of nitrogen started at a level of 3000 m3h-1 and reached 17,500 m3h-1 after 12 hours when the water seal was finished in the tailgate. Due to the nitrogen inertisation the face was opened again after one week without damage to equipment.
The use of nitrogen in France rose in the 1980s. The maximum annual consumption of evaporated nitrogen in H.B.L. (Houilleres du Bassin de Lorrain), reached 16.4 million m3 of nitrogen gas in 1982 and 9.9 million m3 in 1983 in Blanzy (Casadamont, 1986). A special nitrogen pipeline, Azoduct, was built by H.B.L. in 1986. The Azoduct connected the chemical plant Air Liquide 40km from Richemont with the mines La Houve, Vouters, Reumaux, and Simon and supplied them with nitrogen gas with a purity of 99.8% and flow rates in a range up to 10,000 m3h-1. The consumption averages between 20-25 million m3 per year. The greatest annual consumption of 42.24 million m3 was in 1989 due to the fighting of an underground fire (Dupond, 1990). In the French coalfield nitrogen is primarily used for the control of spontaneous combustion. The flow rate of nitrogen is usually 2,000 m3h-1 per face when 10ppm of CO occurs.
THE FORMER SOVIET UNION STATES
The theory of the inertisation of mine fires was described by Sucharevskij (1952), who recommended the use of nitrogen, and three cases of inertisation by carbon dioxide in the Donetsk Coal Basin are described. Kessarijskij (1969) wrote that nitrogen mobile evaporators units AGU-2M and AGU-6 were used in Russian mines in the 1960 s. A mobile liquid tank and evaporator unit AGU-2M is described in the mines rescue handbook (Glavkov, 1988) as standard equipment with an output of 345 m3h-1 of nitrogen gas and a 1440 kg liquid nitrogen tank.
At the No.29 mine of the coal producer Vorkutaugol in Siberia there occurred an underground fire in June 1968 (Osipov, 1970). The fire occurred after blasting and the sealed district had a volume of approximately 100,000 m3. Four nitrogen units of the type AGU-2M were required for inertisation. The injection started on the 29th of September 1968. 179,400 m3 of nitrogen gas were injected during a period of 164 hours with flow rates in the range of 11-32 m3 min-1. After inertisation, the fire area was sealed for 8 months and then re-opened.