Published : Proceedings of The First International Mine Environment and Ventilation Symposium. Indian School of Mines Dhambad 11-12 December 2000, ISBN 81-204-1458-6.

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EXPERIENCE OF THE USE OF NITROGEN

AND FOAM TECHNOLOGY INTHE CZECH COAL MINES

Dr. A.Adamus, MinE

Associate Professor, Institute of Safety Engineering,

VSB - Technical University Ostrava, 17. Listopadu Street,

708 33 Ostrava-Poruba, Czech Republic,

It was on the 8th of August 1949, when nitrogen inertization of an underground fire was first used at the Doubrava Mine in the Czech part of the Upper Silesian Coal field. Since then many countries have used nitrogen for fighting, suppression and prevention ofunderground fires. This paper reviews experience of the use of nitrogen in the Czech Republic. Special attention is paid to the first use of nitrogen in the Czech Republic, being probably the first instance of the use of pure nitrogen for fighting a mine fire. The present day use of nitrogen, its sources, consumption and technological equipment, include isofoam technology is reviewed.

USE OF NITROGEN AT THE DOUBRAVA MINE, 1949

In the Czech Republic,the first time nitrogen was used for fighting a mine fire in the Ostrava-Karvina Coal basin after a methane explosion at the Doubrava mine (Hajek 1969, Adamus1995). The methane explosion 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 mine shafts at the surface, two downcast and two upcast. The shafts ware sealed with airtight plugs covered with clay and a layer of sand. The Czech patent 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 on the direction of Mr. Artur Kanczucky, the mine director, who chose this method for returning the mine to production. A cryogenic nitrogen generator 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 - 3.0 MPa 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 (10-11 m3 min-1) with an output temperature + 9 0C. The nitrogen gas was delivered to the shaft by a pipeline, with a diameter of 100 mm, and by drill rods with diameters of 100 mm down the shaft to a level of 540 m.

NITROGEN INERTIZATION - TODAY EXPERIENCE

The knowledge obtained through the use of nitrogen at the Doubrava mine was used with success by mines rescue teams in the Ostrava-Karvina Basin (OKB). Three pressure bottle trailers containing 630 m3 each were manufactured and delivered to the Central Mines Rescue Station at the OKB in 1957. The pressure bottle trailers of 945 m3 capacity were bought later. Nitrogen gas transported by pressure trailers was used for suppression of heating and inertization of balancing chambers (permeate chambers). Two types of Russian liquid nitrogen mobile tankers, type STK, of 2.5 m3 and 5.0 m3 capacity (0.25 MPa) were bought in 1979.

Two types of transportable liquid nitrogen containers of 500 and 1000 litre were made by FEROX Decin, Czech Republic, and were bought in 1980. Since 1986 15 m3 liquid nitrogen mobile tankers of the type TN 15 /FEROX Decin/ have been used. Liquid nitrogen technology has been used in the prevention of spontaneous combustion of coal since 1979, by the use of nitrogen flushing. For fighting mine fires, the Central Mine Rescue Station of Ostrava in OKB bought a jet turbine, type GIG 4 made in Ukraine, which produces 340 m3 min-1 of inert exhaust gases.

A mobile evaporator type MOD 200, which produces 200 m3 min-1 of nitrogen gas, was manufactured for the Central Mines Rescue Station in Most in 1984. The evaporator is supplied with liquefied nitrogen by a mobile tanker TN 15. The same mobile evaporator was manufactured for the Central Mines Rescue Station in Kladno in 1989.

Progress in the use of nitrogen inertization continued in 1988 by the building of evaporation stations, three at the mines in OKB, in the North Bohemia Coal Basin three stations and in the Kladno Coal Basin two stations. They were equipped with a 15-20 m3 liquid nitrogen storage tank and 15-20 m3 min-1 nitrogen air evaporators. The purpose of these stations has been, above all, to supply the mines with nitrogen gas for the control of spontaneous combustion. For the same reason in 1989 equipment based on molecular sieves, PSA system, type CMS600 made in Germany and manufactured by the INGA company, which produces 10 m3 min-1 of 98 % concentrated nitrogen gas was acquired. Later, another PSA nitrogen generator, type CMS 900, which produces 15 m3 min-1 of nitrogen gas, was bought. Both molecular sieves are working in the OKB at present.

The consumption of nitrogen has been steadily rising in the OKB, for this reason a central nitrogen pipeline connecting the OKB mines and the steelworks Nova Hut Ostrava, utilising the nitrogen produced as a by-product of the production of oxygen, was constructed. The central nitrogen pipeline of the OKB was opened in April of 1993 and it is the main source of nitrogen in the OKB today.

The reduction in the Czech coal industry output (- 53 % sinc e 1985 to 1999) has not reduced the consumption of nitrogen. Along with the closure of some mines have also closed some evaporation stations, but the general consumption of nitrogen is still rising due to the existence of the central nitrogen plant in the Ostrava-Karvina Basin. The total consumption of nitrogen in the Czech mines in the years 1949-1999 reached 424 mil. m3 (58.3 mil. in 1999).

The North-Bohemia Brown Coal Basin uses the most liquid nitrogen. The consumption of nitrogen in the years of 1981-1963 was 5.84 mil m3 of nitrogen gas. From it was used 63 % for prevention and 37 % for suppression of fires. This basin consumed 52,000 m3 of nitrogen in 1998 (recalculated to gaseous nitrogen). The Kladno Coal Basin uses liquid nitrogen. There was used 1.926 mil. m3 of nitrogen gas (60 % for prevention and 40 % for suppression of mine fires and coal storage) in the years of 1984-1994. In 1994 their consumption of nitrogen was 109,500 m3 (recalculated to gaseous). There have been nitrogen used only occasionally during last five years.

The highest nitrogen consumption is in the Ostrava-Karvina Coal Basin. The central nitrogen pipeline produces nitrogen with a concentration of 99 %. In December 1997 were installed two polymer membrane units of the Generon type by Messer at the start of the pipeline which supports the prevention mode of the pipeline by adding 2000 m3h-1 of the nitrogen. Output during prevention mode is up to 7000 m3h-1 of nitrogen gas continuously, for the control of spontaneous combustion. When in the suppression mode, the pipeline provides 300 m3min-1 of nitrogen gas for a period up to10 hours with a maximum input pressure of 1,6MPa. The total length of the pipeline on the surface is 45 km. The distance between the nitrogen source and the first mine Dukla is 13.5 km to the west. This main branch has a diameter of 300 mm, the branches between the mines have a diameter of 150-250 mm, and the main subsurface branches have a diameter of 150 mm. The Central Mine Rescue Station in Ostrava has 2000m flexible hoses, of the type NITROGEN, made in Germany by PARSCH, with a diameter of 150 mm and working pressure of 1.5 MPa. The nitrogen is usually used in Ostrava-Karvina Basin for the control of spontaneous combustion. Nitrogen is released through unrecoverable branches, which are situated in the waste 30-50 m behind a face, with about an 8-15 m3 min-1 nitrogen infusion flow rate. The recommended nitrogen infusion flow rate for the control of waste spontaneous combustion in the Ostrava-Karvina Basin is 10-15 m3 min-1. An optimisation of a nitrogen inertization of wastes has been solved at the VSB-Technical university Ostrava, Institute of safety engineering, and results have been published in (Adamus, 1997). The specific consumption of the nitrogen gas in OKB reached 5,073 m3 t-1 in 1999, recalculated under total output of OKB, include mines, which do not use nitrogen.

THE APPLICATION OF THE FOAM TECHNOLOGY

The objective gob inertization with gaseous nitrogen in to obtain threshold oxygen concentration in the spontaneous combustion process in a critical zone of a longwall face gob. The resent research shows (Adamus 1997) that a threshold oxygen concentration for spon-com of coal in the Ostrava-Karvina Coal Basin is 6 %. The incubation period of spon-com is usually 6 weeks in Ostrava-Karvina Coal Basin .It is recommended to reduce the oxygen concentration in a gob to 11 %. It is very difficult to obtain this value of the oxygen concentration in a critical zone of a gob just by means of the gaseous nitrogen in longwall faces with high output. Therefore, further steps to reduce a gob permeability have been adapted.

One of the methods to increase aerodynamic resistance of a gob is foam application for gob foaming to prevent air leakage through a gob. Applied technology of gob foaming by means of nitrogen detergent foam that had been injected to a gob (Voracek 1994)was used in Ostrava-Karvina Coal Basin as early as in 1992. The effect of detergent foam in gob is usually inhibition and due to relatively short lifetime of the detergent foam, the products (two-komponent isofoam) manufactured by EKOCHEM, S.A. Katowice (Poland) are used to reduce ventilation of gobs in some cases. The whole range products manufactured by this company was being gradually approved for the application in mines in the Czech Republic in 1994 - 1997 including: regular Krylamina foam, extra-light foam, Ekofoam, DU Krylamina glue, DU/S Krylamina glue, lumping set to be used with the EKOCHEM “Hydrox-Adal” products and component transportation containers. The application of a two-component Krylamina foam was approved by the Mining Authorihy and Hygienic Department of the Czech Republic as well as by the mines in the Ostrava-Karvina Coal Basin and mines in the Mostecka Coal Company S.A. in the Northern Czech Brown Coal Basin.

The regular Krylamina and extra-light Krylamina type foam are a two-component materials made of water solution of acrylic-urea resins with modified additive of 1,1 - 1,2 g.cm-3, pH 7,5 - 9,5 and transparent yellow-beige catalyst of 1,1 - 1,03 g.cm-3, pH 2,5 - water solution of the orthophosphoric acid with foam agents and modifiers. They feature very low emission of free formaldehyde, good anti-electric properties, increased strength and sufficient elasticity. Krylamine foams are produced on the application spot by means of compressed air foaming or foaming equipment. A foaming gun produces regular light foam - mixing ratio 4:3, 20-40-fold foaming or extra-light foam - mixing ratio 1:1, 30-50-fold foaming. Produced foam is flexible. The foam might be applied to fill selected spaces, it becomes flexible after 5 minutes, it reaches full insulating properties after 24 hours. When the environment humidity is higher than 70% it does not change its volume. The lifetime of the extra-light foam is limited - after three weeks the properties of foam deteriorate. The “regular” foam is ageing-resistant, the minimum period when it does not change its capacity is 12 month and is elastic. Average measuring density of dry foam is 3-5 kg.m-3.

The “Hydrox-Adal” pumping set includes :

  • two-circuit compressed air force pump of the design that makes it possible to change the ratio of forced media capacity in specific circuits,
  • force route for separate resin and catalyst forcing for a pump to a mixing spot,
  • mixer with infection head,
  • foaming gun.

The pump capacity is 14l/min. Foam production components are transported in 30-liter containers. Pumping set is mobile, two operators are sufficient to operate it.

“Extra-light” foam is used to seal longwall gobs to increase aerodynamic resistance of a gob and prevent endogenous fires of coal. It can be used for cavity filling where is a threat of explosive gas accumulation. Regular foam is used to fill the cavities above longwall face support, narrow working sealing, pack strip fillings, ceiling sealing, insulating and air stoppings. Foams allow fast and easy application and efficient sealing. Walls of the cavities to be filled can be both dry or wet.

“Krylamine” INJECTION IN THE LONGWALL NO. 139702 IN THE Lazy OKD, a.s. IN Orlova COAL MINE

The seam no. 512 of Karvina layers of the 5,5 m thickness was extracted by Panda shearer (CdF), Gerlach conveyor and Dynatrac chainless vehicle in December 1995 in the longwall face no.139702. There was an incident of spontaneous combustion of coal and the longwall face was sealed with fire stops. The longwall face was opened and extraction restarted on 12 April 1996, but due to the symptoms of endogenous fire it was sealed again on 22 April 1996 after the progress of 22 meters. While the symptoms of endogenou fire appeared, the longwall face was inertized with gaseous nitrogen. 1,2 mil m3 of gaseous nitrogen was used for inertization up to 30 May 1996.

The longwall face was opened again on 15 June 1996 with immediate extraction. Accumulation of CO was noticed in the upcast in the afternoon on 18 June 1996. It was possible to determine that the situation got stabilized due to tremendous effort that was caused by a complicated case of spontaneous ignition on 20 June 1996. The Krylamina foam together with gaseous nitrogen inertization played major role in fighting endogenous fire that appeared in the longwall face no. 139702 in the Lazy Coal Mine in the Ostrva-Karvina Coal Basin that was extracted. Krylamina foam was used to seal longwall face gobs at the caving line in both roads in a full profile continuously together with gaseous nitrogen inertization at the volume flow of 20m3.min -1. The Krylamina foam helped to reduce a gob permeability and obtain higher efficiency of gaseous nitrogen inertization.

CONCLUSIONS

The existing experience in nitrogen application in mines in the Czech Republic are in fact identical with the existing experience published in the literature (Both 1981, Garg 1978,1987, Harris 1981, Casadamint 1986). Nitrogen can be successfully applied to prevent and inhibit fires. We cannot conclude however, that application of this technology may eradicate fires completely. Therefore, it is reasonable to use together with nitrogen inertization other prevention and inhibition methods. One of the possibilities to increase the efficiency of nitrogen inertization is the application of filling foam materials for gob foaming. The two-component Krylamina foam is used for this purpose in the Ostrava.Karvina Coal basin.

THE AUTHOR PROPOSITION

The author proposes a discussion on the theoretical and practical details of the experience of the use of nitrogen in mines and the historical verification of the usage of Nitrogen. Proposals of technical co-operation or of the holding of a conference or any ideas, information or suggestions can be sent to the e-mail addresses: .

Literature

Adamus, A., Hajek, L., Posta, V. (1995), A Review of Experience on The Use of Nitrogen in Czech Coalmines. Proceedings of the 7th US Mine Ventilation Symposium, Lexington, June 1995, pp 237-241.

Adamus, A., Vlcek, J. (1997), The Optimisation of the Nitrogen Infusion Technology. Proceedings of the 6th International Mine Ventilation Congress, Pittsburgh, May 1997.

Adamus, A., Veznikova, H. (1997) The Influence of the Nitrogen Inertization to a Kinetic of the Spontaneous Combustion of Coal. Research report of the project no. GACR 105/95/1111, VSB-TU Ostrava, January 1997.

Both,W.(1981), Fighting Mine Fires with Nitrogen in the German Coal Industry. The Mining Engineer, May,1981, pp 797-804.

Casadamont, M.B. (1986), L´utilisation de l´azote dans les travaux du fond. Publications Techniques des Charbonnages de France, No. 3, 1986, pp 1-15.

Garg, P.C., Bhowmick, P.C. (1978), Use of Nitrogen Flushing to Spontaneous Heating – proposals for a Trial in an India Mine, Journal of Mineral, Metal and Fuels, September 1978, pp 315-322.

Garg, P.C. (1987), Development of Nitrogen Infusion Technology for Fighting and Inhibition of Fires. Journal of Mineral, Metal and Fuels, August 1987, pp 368-377,394.

Hajek, L.(1969), Twenty years after Doubrava. Zachranar nr. 2 - 10, 1969

Harris, L. (1981), The Use of Nitrogen to Control Spontaneous Combustion Heatings”, The Mining Engineer June 1981, p.883-892.

Pošta, V., Adamus, A. (1997), Prevention and Inhibition while Fighting Endogenous Fires by Means of Nitrogen and Sealing/filling Material in the Ostrava-Karvina Coal Basin. In. Proceedings of the International Conference of 90th Years of Rescue in Mines on the Teritory of Poland. Bytom, Poland, November 1997.

Voracek,V., Mikosek,R., Miks., Samek,A. (1994), Experience on the Prevention of Spontaneous Combustion of Coal in Longwall Face Gobs with Nitrogen Foam at the Darkov Colliery, the Mine Barbora. In.: Proceedings of the conference “ The Today Problems of the Mining” VSB-Technical University Ostrava, Ostrava 1994, pp. 65-67.