Method for determining incubation period of coal spontaneous combustion

Abstract

FIELD: mining industry.SUBSTANCE: invention can be used to combat spontaneous combustion of coal at coal mining enterprises. A method is proposed for determining the incubation period of spontaneous combustion of coal, which includes measuring the initial temperature of coal, taking coal samples, placing crushed coal in sorption vessels to determine the concentration of oxygen in the sorption vessels, taking into account the specific heat of melting ice for coal at sub-zero temperatures, and calculating the duration of the incubation period of spontaneous combustion of coal. Moreover, according to the invention, the total concentration of gases released from coal in sorption vessels is determined, taking into account which the rate constant of oxygen sorption by coal is determined.EFFECT: increased efficiency of determining the incubation period of spontaneous combustion of coal.1 cl, 1 tbl

Description

[0001] The invention relates to the mining industry and can be used to combat spontaneous combustion of coal at coal mining enterprises.

[0002] A method is known for determining the incubation period of spontaneous combustion of coal by measuring the initial temperature of coal, taking coal samples, determining the average value of the rate constant of oxygen sorption by coal at a temperature from 25°C to and calculating the duration of the incubation period using the formula:

[0003] , (1)

[0004] where: - average heat capacity of coal in the temperature range ; - temperature of coal in the massif; - critical temperature of autoignition; - working moisture content of coal; - latent heat of evaporation of water; - natural gas content of coal; - heat of methane desorption; - the average value of the oxygen sorption rate constant at temperatures from 25°C to ; - proportionality coefficient; - oxygen concentration; - heat of oxygen sorption.

[0005] (Alperovich V.Ya., Chuntu G.I., Pashkovsky P.S. et al. Incubation period of spontaneous combustion of coals. Occupational safety in industry. - 1973. - No. 9. - P. 43-45).

[0006] The disadvantage of the known method is the duration of time and the difficulty of determining the average value of the oxygen sorption rate constant when heating coal from 25°C to due to the intense release of toxic gases when the temperature rises.

[0007] A method is also known for determining the incubation period of spontaneous combustion of coal by measuring the initial temperature of the coal, taking coal samples, determining the value of the oxygen sorption rate constant at a constant temperature and calculating the duration of the incubation period using the formula:

[0008] , (2)

[0009] where: C is the specific heat capacity of the coal accumulation; T к- critical temperature of spontaneous combustion of coal; T0 - initial temperature of coal accumulation; j - heat of evaporation of water; W - initial moisture content of coal accumulation; X - natural gas content of coal; q d - specific heat of methane desorption; α - coefficient of oxygen absorption in air; C0 - oxygen concentration at the entrance to the coal accumulation; q0 - specific heat of oxygen sorption by coal; K Т - the rate constant of oxygen sorption by coal, determined based on the results of measurements using the formula:

[0010] , (3)

[0011] where: M is the mass of the coal sample in the sorption vessel; V is the volume of air in the sorption vessel in contact with the coal; τ is the duration of contact of air with coal; C1 is the initial concentration of oxygen in the air of the sorption vessel; C А - the concentration of oxygen in the vessel after time τ.

[0012] (Instructions for determining the incubation period of spontaneous combustion of coal. Series 05. Issue 38. - M., 2013. - 24 p.).

[0013] The disadvantage of the known method is its low efficiency due to the failure to take into account the influence of negative temperatures of the environment and coal on the spontaneous combustion process, which slow down the spontaneous combustion process due to heat loss due to melting ice and a decrease in the rate constant of oxygen sorption by coal.

[0014] The closest technical solution is a method for determining the incubation period of spontaneous combustion of coal, which includes measuring the initial temperature of coal, taking coal samples, determining the value of the oxygen sorption rate constant at a constant temperature, taking into account the specific heat of melting ice for coal at sub-zero temperatures, and calculating the duration of the incubation period of spontaneous combustion of coal using the formula:

[0015] , (4)

[0016] where: C is the specific heat capacity of the coal accumulation; T к- critical temperature of spontaneous combustion of coal; T0 - initial temperature of coal accumulation; j - heat of evaporation of water; W - initial moisture content of coal accumulation; X - natural gas content of coal; q d - specific heat of methane desorption; α - coefficient of atmospheric oxygen assimilation; C0 - oxygen concentration at the entrance to the coal accumulation; q0 - specific heat of oxygen sorption by coal; g - specific heat of melting of ice, cal / g (taken into account only for coal at sub-zero temperatures); K Т - the rate constant of oxygen sorption by coal (determined at a temperature from 0 to +10°C for coal at sub-zero temperatures, or at a temperature from +15 to +25°C for coal at positive temperatures), is found from the results of measurements using the formula:

[0017] , (5)

[0018] where: M is the mass of the coal sample in the sorption vessel; V is the volume of air in the sorption vessel in contact with the coal; τ is the duration of contact of air with coal; C1 is the initial concentration of oxygen in the air of the sorption vessel; C А - the concentration of oxygen in the sorption vessel after time τ.

[0019] (Safety rules for the processing, enrichment and briquetting of coal" dated October 28, 2020 No. 428 (as amended on December 27, 2023).

[0020] A disadvantage of the known method is its low efficiency due to the failure to account for the effect of gas evolution from the coal in the sorption vessel when determining the rate constant of oxygen sorption by coal. The release of methane, carbon dioxide, and other gases leads to a decrease in the oxygen concentration in the sorption vessel, which causes errors in determining the rate constant of oxygen sorption by coal and the duration of the spontaneous combustion incubation period.

[0021] The technical result of this invention is to increase the efficiency of determining the incubation period of spontaneous combustion of coal.

[0022] The specified technical result is achieved by the fact that in the method for determining the incubation period of spontaneous combustion of coal, which includes measuring the initial temperature of coal, taking samples of coal, placing crushed coal in sorption vessels to determine the concentration of oxygen in the sorption vessels, taking into account the specific heat of melting ice for coal at sub-zero temperatures, and calculating the duration of the incubation period of spontaneous combustion of coal using the formula:

[0023] , (6)

[0024] where: C is the specific heat capacity of the coal accumulation; T к - critical temperature of spontaneous combustion of coal; T0 - initial temperature of coal accumulation; j - heat of evaporation of water; W - initial moisture content of coal accumulation; X - natural gas content of coal; q d- specific heat of methane desorption; α - coefficient of atmospheric oxygen assimilation; C0 - oxygen concentration at the entrance to the coal accumulation; q0 - specific heat of oxygen sorption by coal; g - specific heat of melting of ice, cal / g (taken into account only for coal at sub-zero temperatures); K Т - the rate constant of oxygen sorption by coal, ml / (g⋅h) (determined at a temperature from 0 to +10°C for coal located at negative temperatures, or at a temperature from +15 to +25°C for coal located at positive temperatures), according to the invention, the total concentration of gases released from coal in sorption vessels is determined, and the rate constant of oxygen sorption by coal is found from the results of measurements using the formula:

[0025] , (7)

[0026] where: M is the mass of the coal sample in the sorption vessel; V is the volume of air in the sorption vessel in contact with the coal; τ is the duration of contact of air with coal; C1 is the initial concentration of oxygen in the air of the sorption vessel; C А - oxygen concentration in the sorption vessel after time τ;C S 0 - initial total concentration of gases released from coal in the sorption vessel;C S - the total concentration of gases released from coal in the sorption vessel after time τ.

[0027] To determine the rate constant of oxygen sorption by carbon, sorption vessels are used. The oxygen concentration in the air is first measured, then samples of crushed carbon are added and sealed. During the aging process, the carbon sorbs oxygen, resulting in a decrease in its concentration. After a specified aging time τ (usually 24 hours), the remaining oxygen concentration in the sorption vessel is measured. The initial and final oxygen concentrations are used to calculate the oxygen sorption rate constant.

[0028] However, during coal metamorphism, the organic matter decomposes, producing certain gases. Methane is the most intensely released gas during coal metamorphism, some of which remains in the pores and cracks of the coal. Carbon dioxide accumulates in some grades of coal. Coal mining involves crushing the coal seams, releasing previously accumulated gases into the surrounding atmosphere. The release of gases from coal alters the concentration of gases initially present in the atmosphere, including oxygen.

[0029] In the known method, the rate constant of oxygen sorption by coal is determined using formula (5), which does not take into account changes in the oxygen concentration in the sorption vessel due to gas release from the coal. However, gases such as methane, carbon dioxide, carbon monoxide, hydrogen, and saturated and unsaturated hydrocarbons can be released from crushed coal in the sorption vessel at varying rates. Therefore, the oxygen concentration in the air in the sorption vessel will decrease not only due to its absorption by the coal but also due to the release of previously accumulated gases from the coal. Experience has shown that the concentration of methane released from coal in sorption vessels can reach 30% or more. In such cases, the oxygen concentration is significantly distorted, leading to errors in determining the rate constant of oxygen sorption by coal and in calculating the incubation period of spontaneous combustion of coal.

[0030] To improve the efficiency of determining the incubation period of spontaneous coal combustion, oxygen content and the concentration of gases released from the coal after crushing are determined in air samples taken from sorption vessels before the coal samples are placed in them. These gases include methane, carbon dioxide, carbon monoxide, hydrogen, ethane, propane, butane, ethylene, and propylene. In the atmospheric air contained in the sorption vessels before the coal sample is placed in the sample, carbon dioxide has the highest concentration (approximately 0.05%). The concentrations of gases released from the coal are summed to calculate C S 0.

[0031] Then the carbon is placed in the sorption vessels and sealed. After holding for a specified time τ (usually 24 hours), a gas sample is again taken from the sorption vessels to determine the concentration of oxygen and all released gases (methane, carbon dioxide, carbon monoxide, hydrogen, ethane, propane, butane, ethylene, propylene). The concentrations of gases released from the carbon (methane, carbon dioxide, carbon monoxide, hydrogen, ethane, propane, butane, ethylene, propylene), measured in the air of the sorption vessels after holding the carbon for a specified time τ, are summed to calculate C S Using the obtained results, the oxygen sorption rate constant is calculated using formula (7), and then the duration of the spontaneous combustion incubation period is determined using formula (6).

[0032] The method is as follows.

[0033] At coal plants, coal temperature is measured and coal samples are collected in sealed vessels to determine the rate constant of oxygen sorption by coal. In the laboratory, the coal is crushed. Air samples are taken from the sorption vessels and the oxygen content and concentration of gases released from the coal after crushing (methane, carbon dioxide, carbon monoxide, hydrogen, ethane, propane, butane, ethylene, and propylene) are determined. The concentrations of the released gases are summed to find C. S 0. Coal samples are then placed in the sorption vessels and sealed. After holding for a specified time τ, air samples are again taken from the sorption vessels, and the concentrations of oxygen and gases released from the coal are determined. The concentrations of the released gases (methane, carbon dioxide, carbon monoxide, hydrogen, ethane, propane, butane, ethylene, and propylene) measured in the air samples taken from the sorption vessels after holding for a specified time τ are summed to find C. S The obtained total concentrations of gases released from coal and the oxygen content in the sorption vessels are used to calculate the rate constant of oxygen sorption by coal using the formula:

[0034] ,

[0035] where: M is the mass of the coal sample in the sorption vessel; V is the volume of air in the sorption vessel in contact with the coal; τ is the duration of contact of air with coal; C1 is the initial concentration of oxygen in the air of the sorption vessel; C А - oxygen concentration in the sorption vessel after time τ;C S 0 - initial total concentration of gases released from coal in the sorption vessel;C S - the total concentration of gases released from coal in the sorption vessel after time τ.

[0036] The duration of the incubation period of spontaneous combustion is determined by the formula:

[0037] ,

[0038] where: C is the specific heat capacity of the coal accumulation; T к- critical temperature of spontaneous combustion of coal; T0 - initial temperature of coal accumulation; j - heat of evaporation of water; W - initial moisture content of coal accumulation; X - natural gas content of coal; q d - specific heat of methane desorption; α - coefficient of atmospheric oxygen assimilation; C0 - oxygen concentration at the entrance to the coal accumulation; q0 - specific heat of oxygen sorption by coal; g - specific heat of melting of ice, cal / g (taken into account only for coal at sub-zero temperatures); K Т - the rate constant of oxygen sorption by coal, ml / (g h) (determined at a temperature from 0 to +10°C for coal at sub-zero temperatures, or at a temperature from +15 to +25°C for coal at positive temperatures).

[0039] The claimed method is illustrated in Table 1 (see graphic section), which shows the change in the rate constant of oxygen sorption by coal and the duration of the spontaneous combustion incubation period depending on the sum of the concentrations of the released gases. Experience has shown that methane is the main gas released in Kuzbass coals, the concentration of which in sorption vessels can reach 30% or more after 24 hours.

[0040] The conducted studies showed that, taking into account the total concentration of gases emitted from coal to 30%, the calculated value of the oxygen sorption rate constant by coal decreased by 1.88 times. Accordingly, the duration of the spontaneous combustion incubation period, taking into account gas emissions from coal, increased by 1.33 times. Thus, from Table 1 it follows that, excluding gas emissions from coal, the duration of the spontaneous combustion incubation period was 63.6 days, and the coal is classified as susceptible to spontaneous combustion. When taking into account gas emissions from coal, the duration of the spontaneous combustion incubation period increased to 84.4 days, allowing the coal to be classified as not susceptible to spontaneous combustion. Reclassifying this coal as not susceptible to spontaneous combustion will improve work safety and avoid unnecessary costs for endogenous fire prevention efforts.

[0041] The proposed method will improve the accuracy of calculating the spontaneous combustion incubation period for coal that releases gases during oxygen sorption, thereby enhancing mining safety. At the same time, the costs of preventing spontaneous combustion in coal will be reduced.

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