A coal spontaneous combustion temperature determination method based on carbon isotope values

Abstract

The application discloses a coal spontaneous combustion temperature determination method based on carbon isotope values, first collects residual coal samples to perform spontaneous combustion experiments, measures C 13 carbon isotope values in CO2 generated by the residual coal at different temperatures, then establishes a residual coal coordinate system, marks the measured C 13 carbon isotope values in the coordinate system, then performs relational expression fitting, and finally obtains a mathematical relationship model between residual coal temperature and C 13 carbon isotope values; in subsequent actual monitoring processes, only C 13 carbon isotope values of gas samples in a goaf need to be obtained and substituted into the mathematical relationship model to inversely calculate a temperature value of current residual coal spontaneous combustion; since the CO concentration or the CO2 concentration in the gas sample does not need to be concerned after the gas sample is collected, interference of CO and CO2 released by a vehicle tail gas, blasting operation and the like on monitoring is avoided, and finally, the temperature of coal spontaneous combustion can be more accurately determined to provide data support for subsequent fire prevention and extinguishing measures.

Description

Technical Field

[0001] This invention relates to a method for determining the spontaneous combustion temperature of coal, specifically a method for determining the spontaneous combustion temperature of coal based on carbon isotope values, belonging to the field of coal mine fire prevention and extinguishing technology. Background Technology

[0002] In coal mine goaf areas, large amounts of unrecoverable coal remain, referred to as residual coal. This residual coal may spontaneously ignite in the goaf environment. Currently, there are many methods for determining the degree or temperature of spontaneous ignition in residual coal, such as the spontaneous ignition index gas method. This method involves collecting gas samples from the goaf and analyzing their concentrations to determine the current spontaneous ignition temperature of a particular type of coal. However, because concentration is a relative value and underground coal mine conditions are complex, the concentration of spontaneous ignition index gases can be significantly affected by different conditions. For example, the CO2 naturally present in the coal seam, or CO and CO2 released from underground vehicle exhaust or blasting operations, can lead to large deviations in the results of judging the spontaneous ignition temperature based on CO or CO2 concentration values. This often results in inaccurate judgments, making safety management during coal mining more complex and difficult. Another patent, CN111366686A, discloses a method for determining spontaneous combustion zones in coal mines based on detecting C14 radioactivity. This method involves preparing sodium bicarbonate powder containing radioactive C14, drilling multiple detection holes into the goaf, injecting the sodium bicarbonate powder into the goaf, and observing the C14 radioactivity in the gas collected from each detection hole to determine the spontaneous combustion status of coal in the goaf. However, this method can only determine whether spontaneous combustion exists in the goaf and cannot accurately measure the temperature of residual coal within the goaf. Furthermore, its detection of the goaf relies heavily on the layout of the boreholes, meaning it can only detect the goaf around the boreholes. Therefore, a large number of boreholes are required. Also, because the goaf is large, this method cannot determine spontaneous combustion if spontaneous combustion occurs in areas inaccessible by the boreholes.

[0003] In summary, one of the research directions in this industry is to provide a new method that can monitor the spontaneous combustion of coal in the entire goaf without drilling exploratory boreholes, and at the same time accurately measure the temperature of spontaneous combustion of coal, so as to provide data support for subsequent fire prevention and extinguishing measures. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for determining the spontaneous combustion temperature of coal based on carbon isotope values. This method can monitor the spontaneous combustion of coal in the entire goaf without drilling detection boreholes, and can also accurately measure the temperature of spontaneous combustion, providing data support for subsequent fire prevention and extinguishing measures.

[0005] To achieve the above objectives, the technical solution adopted by this invention is: a method for determining the spontaneous combustion temperature of coal based on carbon isotope values, the specific steps of which are as follows:

[0006] A. Sample Collection and Laboratory Testing: First, residual coal is collected from the goaf area to be monitored, and multiple samples are prepared. Then, spontaneous combustion tests of the coal are conducted in the laboratory. By conducting spontaneous combustion experiments on different samples at different temperatures, the carbon content in CO2 generated by the spontaneous combustion of the residual coal at different temperatures is measured. 13 Carbon isotope values ​​were then used to obtain the corresponding C values ​​for spontaneous combustion of coal at different temperatures. 13 Carbon isotope values;

[0007] B. Establish a mathematical model: with the temperature of the residual coal as the vertical axis, C. 13 A coordinate system is established with carbon isotope values ​​on the horizontal axis, and the corresponding C values ​​at different temperatures obtained in step A are plotted. 13 Carbon isotope values ​​are plotted in this coordinate system, and then a relationship is fitted based on the coordinates of each plotted point. This relationship is the relationship between the temperature of the residual coal and carbon. 13 A mathematical model for the relationship between carbon isotope values;

[0008] C. Gas sampling in goaf: A gas sample is collected once in the goaf or return air corner of the working face using a gas sampler.

[0009] D. Determining the C of the gas sample 13 Carbon isotope values: Using an isotope detection instrument, carbon isotope analysis was performed on the gas sample collected in step C to obtain the carbon content in the gas sample. 13 Carbon isotope values;

[0010] E. Determine the coal's spontaneous ignition temperature: Use the C obtained in step D... 13 The carbon isotope value is substituted into the mathematical relationship model in step B, and the temperature value of spontaneous combustion of the residual coal at the time of this gas sample collection is obtained by calculation through the mathematical relationship model.

[0011] F. Continuous monitoring: Repeat steps C to E at set time intervals, and repeat this process multiple times to obtain the temperature values ​​of spontaneous combustion of residual coal at different collection time points, thereby achieving continuous monitoring of the spontaneous combustion temperature of residual coal in the goaf.

[0012] This invention is based on C 13 The specific principle behind determining the spontaneous combustion temperature of residual coal using carbon isotope values ​​is as follows: As is well known, coal formation takes a long time, and coal formed at different times has different internal carbon content. 13 The carbon isotope values ​​are different; then the inventors discovered that the same coal produces CO2 with different carbon isotope values ​​under different temperatures. 13The carbon isotope values ​​also differed. Based on this discovery, residual coal from the goaf was collected, and a spontaneous combustion experiment was conducted on it beforehand. The carbon content (C) in the CO2 produced by the spontaneous combustion of the residual coal at different temperatures was measured. 13 Carbon isotope values ​​were then used to establish a coordinate system for the remnant coal, ultimately allowing for the fitting of the relationship between the remnant coal temperature and carbon content. 13 A mathematical model of the relationship between carbon isotope values; in subsequent actual monitoring, only C values ​​of gas samples from the goaf need to be obtained. 13 Substituting the carbon isotope values ​​into the above mathematical model allows us to deduce the temperature at which the remaining coal spontaneously ignites.

[0013] Furthermore, the specific formula for fitting the relation in step B is: y = ax 2 +bx+c, where y is the spontaneous ignition temperature of the residual coal, x is the carbon dioxide concentration of CO2. 13 Carbon isotope values, where a, b, and c are constants calculated from experimental data.

[0014] Furthermore, the coefficient of determination R of the fitted relation is calculated. 2 Value, if R 2 If the coefficient of determination is ≥0.9, the relation is retained and determined as a mathematical relation model; otherwise, a new relation is refitted to form a new relation, and the coefficient of determination R of the current relation is recalculated. 2 The value is then repeated until the fitted relationship meets the requirements, thus completing the determination of the mathematical relationship model.

[0015] Furthermore, the time set in step F is no more than 2 hours.

[0016] Compared with existing technologies, this invention first collects residual coal in the goaf, then conducts a spontaneous combustion experiment on it, and measures the C content in CO2 generated by the spontaneous combustion of the residual coal at different temperatures. 13 Carbon isotope values ​​were then used to establish a coordinate system for the remnant coal, and the measured C values ​​were then used to... 13 Carbon isotope values ​​are plotted on a coordinate system, and then a relational fit is performed to ultimately obtain the temperature of the residual coal and the relationship between carbon and carbon content. 13 A mathematical model of the relationship between carbon isotope values; in subsequent actual monitoring, only C values ​​of gas samples from the goaf need to be obtained. 13 Substituting the carbon isotope values ​​into the above mathematical model allows us to deduce the temperature at which the residual coal spontaneously ignites; since only C values ​​are needed after collecting gas samples... 13 Carbon isotope values ​​do not require attention to CO or CO2 concentrations in the gas sample, thus avoiding interference from CO and CO2 released from vehicle exhaust, blasting operations, etc., and ultimately enabling a more accurate determination of the temperature of coal spontaneous combustion, providing data support for subsequent fire prevention and extinguishing measures. Attached Figure Description

[0017] Figure 1This is a schematic diagram of the coordinate system for the fitting relationship in an embodiment of the present invention. Detailed Implementation

[0018] The present invention will be further described below.

[0019] Example: The specific steps are as follows:

[0020] A. Sample Collection and Laboratory Testing: First, residual coal is collected from the goaf area to be monitored, and multiple samples are prepared. Then, spontaneous combustion tests of the coal are conducted in the laboratory. By conducting spontaneous combustion experiments on different samples at different temperatures, the carbon content in CO2 generated by the spontaneous combustion of the residual coal at different temperatures is measured. 13 Carbon isotope values ​​were then used to obtain the corresponding C values ​​for spontaneous combustion of coal at different temperatures. 13 Carbon isotope values ​​are shown in the table below:

[0021]

[0022] B. Establish a mathematical model: such as Figure 1 As shown, with the temperature of the residual coal as the vertical axis and C... 13 A coordinate system is established with carbon isotope values ​​on the horizontal axis, and the corresponding C values ​​at different temperatures obtained in step A are plotted. 13 Carbon isotope values ​​are plotted in this coordinate system, and then a relationship is fitted based on the coordinates of each plotted point. The specific relationship is: y = -0.0898x 2 +2.6428x+148.13, where y is the spontaneous ignition temperature of the residual coal and x is the carbon dioxide content of CO2. 13 The coefficient of determination for carbon isotope values ​​is calculated to be R. 2 =0.9629, meeting the required standard; therefore, the relationship is determined to be the relationship between the temperature of the residual coal and C. 13 A mathematical model for the relationship between carbon isotope values;

[0023] C. Gas sampling in goaf: A gas sample is collected once in the goaf or return air corner of the working face using a gas sampler.

[0024] D. Determining the C of the gas sample 13 Carbon isotope values: Using an isotope detection instrument, carbon isotope analysis was performed on the gas sample collected in step C to obtain the carbon content in the gas sample. 13 Carbon isotope values;

[0025] E. Determine the coal's spontaneous ignition temperature: Use the C obtained in step D... 13 The carbon isotope value is substituted into the mathematical relationship model in step B, and the temperature value of spontaneous combustion of the residual coal at the time of this gas sample collection is obtained by calculation through the mathematical relationship model.

[0026] F. Continuous monitoring: Repeat steps C to E every 1.5 hours, and repeat this process multiple times to obtain the temperature values ​​of spontaneous combustion of residual coal at different collection time points, thereby achieving continuous monitoring of the spontaneous combustion temperature of residual coal in the goaf.

[0027] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for determining the spontaneous combustion temperature of coal based on carbon isotope values, characterized in that, The specific steps are as follows: A. Sample Collection and Laboratory Testing: First, residual coal is collected from the goaf area to be monitored, and multiple samples are prepared. Then, spontaneous combustion tests of the coal are conducted in the laboratory. By conducting spontaneous combustion experiments on different samples at different temperatures, the carbon content in CO2 generated by the spontaneous combustion of the residual coal at different temperatures is measured. 13 Carbon isotope values ​​were then used to obtain the corresponding C values ​​for spontaneous combustion of coal at different temperatures. 13 Carbon isotope values; B. Establish a mathematical model: with the temperature of the residual coal as the vertical axis, C. 13 A coordinate system is established with carbon isotope values ​​on the horizontal axis, and the corresponding C values ​​at different temperatures obtained in step A are plotted. 13 Carbon isotope values ​​are plotted in this coordinate system, and then a relationship is fitted based on the coordinates of each plotted point. This relationship is the relationship between the temperature of the residual coal and carbon. 13 A mathematical model for the relationship between carbon isotope values; C. Gas sampling in goaf: A gas sample is collected once in the goaf or return air corner of the working face using a gas sampler. D. Determining the C of the gas sample 13 Carbon isotope values: Using an isotope detection instrument, carbon isotope analysis was performed on the gas sample collected in step C to obtain the carbon content in the gas sample. 13 Carbon isotope values; E. Determine the coal's spontaneous ignition temperature: Use the C obtained in step D... 13 The carbon isotope value is substituted into the mathematical relationship model in step B, and the temperature value of spontaneous combustion of the residual coal at the time of this gas sample collection is obtained by calculation through the mathematical relationship model. F. Continuous monitoring: Repeat steps C to E at set time intervals, and repeat this process multiple times to obtain the temperature values ​​of spontaneous combustion of residual coal at different collection time points, thereby achieving continuous monitoring of the spontaneous combustion temperature of residual coal in the goaf.

2. The method for determining the spontaneous combustion temperature of coal based on carbon isotope values ​​according to claim 1, characterized in that, In step B, the specific formula for fitting the relation is: y = ax 2 +bx+c, where y is the spontaneous ignition temperature of the residual coal, x is the carbon dioxide concentration of CO2. 13 Carbon isotope values, where a, b, and c are constants calculated from experimental data.

3. The method for determining the spontaneous combustion temperature of coal based on carbon isotope values ​​according to claim 1, characterized in that, Calculate the coefficient of determination R of the fitted relation. 2 Value, if R 2 If the coefficient of determination is ≥0.9, the relation is retained and determined as a mathematical relation model; otherwise, a new relation is refitted to form a new relation, and the coefficient of determination R of the current relation is recalculated. 2 The value is then repeated until the fitted relationship meets the requirements, thus completing the determination of the mathematical relationship model.

4. The method for determining the spontaneous combustion temperature of coal based on carbon isotope values ​​according to claim 1, characterized in that, The time set in step F is no more than 2 hours.

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