A calculation method for the true critical value of CO and its application

Abstract

The present invention discloses a method for calculating the real critical value of CO and its application. The specific method is: pre-buried bundle pipes monitor the gas composition of the goaf to obtain the concentration data of O2 on the air inlet and return air sides of the goaf; the goaf is divided into three zones: non-spontaneous combustion zone, spontaneous combustion zone and asphyxiation zone in combination with the gas distribution law of the goaf and the numerical simulation method, and the goaf leakage intensity and the numerically simulated oxygen concentration of the goaf are calculated according to the gas distribution law, and then the specific positions of the three zones are obtained; the concentration change trend of different gases at different temperatures during the spontaneous combustion of coal is obtained by using a programmed temperature increase experiment; and the real critical value of CO is obtained. This method combines the leakage intensity of the non-spontaneous combustion zone and the spontaneous combustion zone obtained by the three-zone division of the goaf and the programmed temperature increase experiment results. The result can better invert the spontaneous combustion of the coal left in the goaf of the working face, and the derived critical value can be used as an early warning prompt to prevent spontaneous combustion in the goaf.

Description

Technical Field

[0001] The invention belongs to the technical field of natural fire early warning in mining areas, and in particular relates to a method for calculating a real critical value of CO and an application thereof. Background Art

[0002] If the development system or mining method of coal mines is not designed reasonably in production practice, the possibility of spontaneous combustion of coal will be greatly increased. The occurrence of spontaneous combustion of coal may affect production at the least, burn coal resources and mine equipment at the worst, and even more seriously may ignite gas and coal dust explosions, causing serious accidents with casualties. The economic and resource losses caused by this are often unquantifiable, and the emotional and psychological damage to miners is also quite serious.

[0003] At present, in order to prevent the spontaneous combustion of coal seams, coal mines mainly use bundle tube monitoring systems to grasp the spontaneous combustion of coal seams in goaf areas. The selection of natural combustion marker gases basically includes CO, alkanes, alkenes and alkynes, and the main content of the investigation is the critical temperature of the marker gas generation. Although this method can provide reference significance for coal mines to control and prevent spontaneous combustion in goaf areas to a certain extent, there is no clear standard in the industry to require a safe value for the concentration of marker gas. In actual production applications, coal mine workers usually need to combine the actual production situation, and there is no specific marker gas concentration judgment standard. When the marker gas appears, the natural combustion situation is predicted based on production experience, which will lead to misjudgment of the actual spontaneous combustion situation in the goaf. Therefore, there is an urgent need for a standard method to provide theoretical support for predicting the ignition situation in the goaf area and solve the problem of timely warning and prevention of spontaneous combustion of coal in the goaf area. Summary of the invention

[0004] Technical problems solved: In response to the above technical problems, the present invention provides a calculation method for the true critical value of CO and its application, which solves the problem of possible misjudgment of the spontaneous combustion marker gas in the goaf and improves the accuracy of the use of the marker gas, thereby accurately predicting the spontaneous combustion of coal in the goaf.

[0005] Technical solution: A method for calculating the true critical value of CO, comprising the following steps:

[0006] S1. The pre-buried bundle pipe monitors the gas composition in the goaf and obtains the O2 concentration data on the air inlet and return air sides of the goaf;

[0007] S2. Combining the gas distribution law of the goaf and the numerical simulation method, the goaf is divided into three zones: non-spontaneous combustion zone, spontaneous combustion zone and asphyxiation zone. The air leakage intensity of the goaf and the oxygen concentration of the goaf by numerical simulation are calculated according to the gas distribution law, and the specific positions of the three zones are obtained.

[0008] S3. Using programmed temperature experiments to obtain the concentration trends of different gases at different temperatures during coal spontaneous combustion;

[0009] S4. The calculation formula for the true critical value of CO is as follows:

[0010]

[0011] Where P CO (T) is the true critical value of CO on the return air side, ppm; A is the fire area of ​​the goaf, m 2 ; h is the thickness of coal left in the goaf, m; Q1 is the air leakage in the non-spontaneous combustion zone on the return air side, cm 3 / s; Q2 is the air leakage of the spontaneous combustion zone on the return air side, cm 3 / s;C CO (T) is the CO concentration on the return air side at temperature T, ppm; is the C2H4 concentration on the return air side at temperature T, ppm; is the C2H6 concentration on the return air side at temperature T, ppm; is the C3H8 concentration on the return air side at temperature T, ppm.

[0012] Preferably, the measuring points in step S1 are set on the return air side and the air inlet side of the goaf, and the upper and lower drifts are monitored simultaneously during monitoring, and move synchronously with the advancement of the working face.

[0013] Preferably, in step S1, the monitoring is terminated when the measuring point enters the goaf by 240 m or the oxygen concentration drops to 8 vol.%.

[0014] Preferably, step S2 comprises the following steps:

[0015] S2-1. Based on the data monitored by the bundle tube, the trend of oxygen concentration on the air inlet side and the air return side with the burial depth is obtained;

[0016] S2-2. Calculate the goaf leakage intensity and the ultimate leakage intensity on the air inlet side and the return air side;

[0017] S2-3. Numerical simulation of goaf;

[0018] S2-4. The three zones are divided according to the field measurement results, numerical simulation results, calculation results of air leakage intensity in goaf and calculation results of ultimate air leakage intensity in goaf.

[0019] Preferably, the calculation method of the goaf air leakage intensity and the limit air leakage intensity in step S2-2 is as follows:

[0020] Air leakage intensity in goaf:

[0021]

[0022] In the formula, is the oxygen concentration of fresh air flow, which is 9.375×10 -6 mol / cm 3 ; The oxygen consumption rate when the coal temperature is T and the oxygen concentration is 21 vol.% is determined experimentally, mol / (s×cm 3 ), The mined area x i Air leakage intensity at , cm 3 ·(cm -2 ·s -1 ); x i+1 、x i are the distances between two points in the goaf and the working face, m;

[0023] Limit oxygen concentration in goaf:

[0024]

[0025] Limit air leakage intensity of goaf:

[0026]

[0027] In the formula, is the oxygen concentration of fresh air flow, which is 21 vol.%; q0(T m ) indicates the oxygen concentration is (i.e. 21vt.%) when the heat release intensity; λ e is the thermal conductivity of floating coal, J·s -1 cm -1 ; T m is the highest temperature in the coal body, °C; T y is the rock formation temperature, °C; T g is the air flow temperature, ℃; h is the floating coal thickness, cm; ρ g is the air flow density at the working surface, g·cm -3 ;c g is the heat capacity, J·g -1 ℃ -1 ; x is the distance between the goaf and the working face, cm; C min is the limiting oxygen concentration; is the ultimate air leakage strength, cm 3 ·(cm -2 ·s -1 ).

[0028] Preferably, the division basis of the three zones of the goaf in S2-4 is:

[0029] Non-spontaneous combustion belt:

[0030] Spontaneous combustion belt:

[0031] Choking belt:

[0032] In the formula, is the air leakage intensity of goaf, cm 3 ·(cm -2 ·s -1 ); is the ultimate air leakage strength, cm 3 ·(cm -2 ·s -1 ); is the oxygen concentration; C min is the limiting oxygen concentration in the goaf.

[0033] Preferably, the air leakage of the non-spontaneous combustion belt on the return air side is:

[0034]

[0035] The air leakage of the spontaneous combustion zone on the return air side is:

[0036]

[0037] Where S1 is the non-spontaneous combustion zone side area of ​​the goaf on the return air side, cm 2 ; S2 is the side area of ​​the spontaneous combustion zone on the return air side, cm 2 ; is the average value of air leakage intensity in the non-spontaneous combustion zone of the goaf on the return air side, cm 3 ·(cm -2 ·s -1 ); is the average value of air leakage intensity in the non-spontaneous combustion zone of the goaf on the return air side, cm 3 ·(cm -2 ·s -1 ); Q1 is the air leakage volume of the non-spontaneous combustion zone on the return air side, cm 3 / s; Q2 is the air leakage of the spontaneous combustion zone on the return air side, cm 3 / s.

[0038] The application of the CO real critical value in early warning of spontaneous combustion of coal in goaf areas.

[0039] Beneficial effects: The present invention can solve the problem that there is no clear concentration regulation for the marker gas in the coal mining industry by calculating the real critical value of CO. At the same time, when CO is detected in the upper corner, the calculated data can be compared to accurately grasp the fire area in the goaf, and more reasonable coal fire prevention and extinguishing measures in the goaf can be formulated in time. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1This is a diagram of the arrangement of observation points in three zones of the goaf of the working face according to an embodiment of the present invention;

[0041] Figure 2 This is a graph showing the trend of O2 concentration changes on the return air side of an embodiment of the present invention;

[0042] Figure 3 is a graph showing the change trend of O2 concentration on the air inlet side according to an embodiment of the present invention;

[0043] Figure 4 is a graph showing a change trend of air leakage intensity on the return air side according to an embodiment of the present invention;

[0044] Figure 5 is a graph showing a trend of air leakage intensity variation on the air inlet side according to an embodiment of the present invention;

[0045] Figure 6 Schematic diagram of oxygen volume fraction in goaf area numerically simulated in an embodiment of the present invention;

[0046] Figure 7 This is a schematic diagram of the distribution of the "three zones" in the goaf according to an embodiment of the present invention;

[0047] Figure 8 This is a trend diagram of CO and CO2 concentration changes in a programmed temperature experiment in an embodiment of the present invention;

[0048] Fig. 9 This is a trend diagram of hydrocarbon gas concentration variation in a programmed temperature experiment in an embodiment of the present invention;

[0049] Fig.10 This is a comparison chart of the true critical value of CO and the trend of CO concentration change in the programmed temperature experiment in the embodiment of the present invention;

[0050] Fig.11 This is a schematic diagram of the change of critical value of CO in a small area of ​​high temperature overfire in a goaf according to an embodiment of the present invention;

[0051] Fig.12 It is a schematic diagram of the change of critical value of CO for slow spontaneous combustion over a large area in goaf according to an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0053] Example 1

[0054] The specific implementation steps of this embodiment are as follows:

[0055] (1) Pre-buried bundle pipes monitor the gas composition in the goaf and obtain O2 concentration data on the air inlet and return sides of the goaf

[0056] Four measuring points are set on the return air side of a certain goaf, and the interval between each measuring point is 60m. The measuring points are numbered 1, 2, 3, and 4. Four measuring points are set on the air inlet side, and the measuring points are numbered 5, 6, 7, and 8. Maintain 4 measuring points on the return air side and 4 measuring points on the air inlet side inside the goaf, and observe the upper and lower drifts simultaneously. The daily measuring points move forward with the advancement of the working face. When each measuring point enters the goaf by 240m, or the oxygen concentration drops to 8vol.%, the observation can be ended, so that the O2 concentration data on the air inlet and return air sides of the goaf can be obtained. The specific layout positions of the embedded bundle pipe monitoring points are as follows: Figure 1 shown.

[0057] (2) The goaf is divided into three zones based on the gas distribution law and numerical simulation method. The specific locations of the three zones are obtained based on the goaf leakage intensity calculated by the gas distribution law and the oxygen concentration in the goaf simulated by numerical simulation.

[0058] Through the bundle tube monitoring of the gas change law in the goaf, it is found that Figure 2 Middle return air side and Figure 3 Variation trend of oxygen concentration on the air inlet side with burial depth.

[0059] Using the measured oxygen concentration distribution law in the goaf, the goaf leakage intensity and the limit leakage intensity on the air inlet and return sides can be calculated:

[0060] The relationship between air leakage intensity and oxygen concentration is:

[0061]

[0062] In the formula, is the oxygen concentration of fresh air flow, which is 9.375×10 -6 mol / cm 3 ; The oxygen consumption rate when the coal temperature is T and the oxygen concentration is 21 vol.% is determined experimentally, mol / (s×cm 3 ), The mined area x i Air leakage intensity at , cm 3 ·(cm -2 ·s -1 ); x i are the distances between two points in the goaf and the working face, m.

[0063] The calculation method of limiting oxygen concentration in goaf is:

[0064]

[0065] The calculation method of the ultimate air leakage intensity of the goaf is:

[0066]

[0067] In the formula, is the oxygen concentration of fresh air flow, which is 21 vol.%; q0(T m ) indicates the oxygen concentration is (i.e. 21vt.%) when the heat release intensity; λ e is the thermal conductivity of floating coal, J·s -1 cm -1 ; T m is the highest temperature in the coal body, °C; T y is the rock formation temperature, °C; T g is the air flow temperature, ℃; h is the floating coal thickness, cm; ρ g is the air flow density at the working surface, g·cm -3 ;c g is the heat capacity, J·g -1 ℃ -1 ; x is the distance between the goaf and the working face, cm; is the limiting oxygen concentration; is the ultimate air leakage strength, cm 3 ·(cm -2 ·s -1 ).

[0068] Using formula (1), formula (2) and formula (3), we can calculate the goaf air leakage intensity, goaf limit oxygen concentration and goaf limit air leakage intensity respectively. Figure 4 and Figure 5 .

[0069] Since the oxygen concentration at the measured point in the goaf on the air inlet side is relatively high, it cannot be used to divide the "three zones" of spontaneous combustion in the goaf. The flow field calculation on the air inlet side is carried out with the help of numerical simulation methods: the goaf of the working face is numerically simulated with the help of Fluent software based on the on-site monitoring data, and the range of the "three zones" of spontaneous combustion in the goaf is comprehensively determined based on the simulated goaf oxygen concentration combined with the on-site oxygen concentration measurement results. The results of numerical calculation are as follows Figure 6 As shown, it can be used to assist in dividing the three-band range on the air inlet side.

[0070] The basis for dividing the "three zones" of goaf areas is:

[0071] Non-spontaneous combustion belt:

[0072] Spontaneous combustion belt:

[0073] Choking belt:

[0074] In the formula, is the air leakage intensity of goaf, cm 3 ·(cm-2 ·s -1 ); is the ultimate air leakage strength, cm 3 ·(cm -2 ·s -1 ); is the oxygen concentration; C min is the limiting oxygen concentration.

[0075] According to the field measurement results of the return air side of the working face, the numerical simulation results of the air inlet side, the calculation results of the air leakage intensity in the goaf area, and the calculation results of the ultimate air leakage intensity in the goaf area, the "three zones" are divided as follows:

[0076] Air inlet side: The "three zones" are divided according to the O2 concentration upper limit of 18 vol.% and the lower limit of 9 vol.%, and the width of the spontaneous combustion zone on the air inlet side is 170m~176m.

[0077] Return air side: The spontaneous combustion zone has an upper limit of 18 vol.% and a lower limit of 9 vol.%, and a width of 37m to 137m. The distribution of the "three zones" of the goaf delineated based on the on-site oxygen concentration observation results of the return air side measuring points, the numerical simulation results of the air inlet side and their trend lines is as follows: Figure 7 shown.

[0078] (3) Using programmed temperature experiments to obtain the gas generation law during coal spontaneous combustion

[0079] The natural combustion process of coal is simulated by experimental instruments. After taking coal samples from the working face, they are crushed and screened to obtain particles smaller than 0.15 mm as experimental coal samples, and programmed heating is performed under experimental conditions. Figure 8 and Fig. 9 As shown, the concentration trends of CO, CO2 and hydrocarbon gases are analyzed, and CO is preferably selected as the spontaneous ignition marker gas.

[0080] (4) Inversion of coal combustion state in goaf using the critical value of return air corner CO

[0081] Using formula (1) to calculate the air leakage intensity on the air intake side and the return air side, when the air leakage intensity is set to the average value and the thickness of the coal deposit is 0.3m, according to the side area of ​​the non-spontaneous combustion zone and the spontaneous combustion zone of the goaf, the air leakage volume of the non-spontaneous combustion zone of the goaf on the return air side can be calculated as:

[0082]

[0083] The air leakage volume of the spontaneous combustion zone in the goaf on the return air side is:

[0084]

[0085] Where S1 is the non-spontaneous combustion zone side area of ​​the goaf on the return air side, cm 2; S2 is the side area of ​​the spontaneous combustion zone on the return air side, cm 2 ; is the average value of air leakage intensity in the non-spontaneous combustion zone of the goaf on the return air side, cm 3 ·(cm -2 ·s -1 ); is the average value of air leakage intensity in the non-spontaneous combustion zone of the goaf on the return air side, cm 3 ·(cm -2 ·s -1 ); Q1 is the air leakage volume of the non-spontaneous combustion zone on the return air side, cm 3 / s; Q2 is the air leakage of the spontaneous combustion zone on the return air side, cm 3 / s.

[0086] According to the programmed temperature experiment, the temperature is increased from 30℃ to 200℃, and the concentrations of various gases (CO, C2H4, C2H6, C3H8) at different temperatures are obtained. Their changing trends can be fitted into functional equations respectively. Then the functions of various gas concentrations changing with temperature are:

[0087] C CO (T) = 9E-06T 4 -0.0034T 3 +0.4394T 2 -23.154T+404.16 (10)

[0088]

[0089]

[0090]

[0091] C CO (T) is the CO concentration on the return air side at temperature T, ppm; is the C2H4 concentration on the return air side at temperature T, ppm; is the C2H6 concentration on the return air side at temperature T, ppm; is the C3H8 concentration on the return air side at temperature T, ppm.

[0092] Combined with the known return air leakage and various gas concentrations, the actual critical value of CO generation on the return air side at different temperatures for different fire areas can be calculated as follows:

[0093]

[0094] Right now:

[0095]

[0096] Where P CO(T) is the true critical value of CO on the return air side, ppm; A is the fire area of ​​the goaf, m 2 ; h is the thickness of the remaining coal in the goaf, m.

[0097] The above-mentioned true critical value of return air corner CO can be used to infer the combustion state of the coal left in the goaf, and then warn of the occurrence of spontaneous combustion of the coal left in the goaf.

[0098] The specific application method is as follows: Assuming the fire area is 1m 2 , compare the calculated CO real critical value and the trend of CO concentration changing with temperature in the programmed temperature experiment, such as Fig.10 As shown in the figure, with the increase of temperature, the change trend of the true critical value is the same as the change trend of the CO concentration in the programmed temperature experiment. Compared with the programmed temperature experiment, when the temperature reaches 100°C, the CO concentration in the programmed temperature experiment is 4.15ppm. According to this data, the coal in the goaf is only slowly oxidized at this time; however, according to the true critical value, its growth rate is significantly accelerated, indicating that the coal in the goaf has begun to spontaneously combust.

[0099] At the same time Fig.11 , the real critical value of CO when a small area of ​​spontaneous combustion zone in the goaf is over-burned at high temperature is given, that is, when the temperature is 100℃-200℃, the over-burned area is 2m 2 、3m 2 and 5m 2 The true critical value of CO at Fig.12 The real critical value of CO when the spontaneous combustion zone in the goaf is large and slow spontaneous combustion is given, that is, when the temperature is 30℃-110℃ and the fire area is 15m 2 、17m 2 and 20m 2 When CO is detected in the upper corner, the data in the figure can be compared to accurately grasp the burned area in the goaf and formulate more reasonable prevention and control measures.

Claims

1. A method for calculating the true critical value of CO, characterized in that: The steps include: S1. The pre-buried bundle pipe monitors the gas composition in the goaf and obtains the O2 concentration data on the air inlet and return air sides of the goaf; S2. Combining the gas distribution law of the goaf and the numerical simulation method, the goaf is divided into three zones: non-spontaneous combustion zone, spontaneous combustion zone and asphyxiation zone. The air leakage intensity of the goaf and the oxygen concentration of the goaf by numerical simulation are calculated according to the gas distribution law, and the specific positions of the three zones are obtained. S3. Using programmed temperature experiments to obtain the concentration trends of different gases at different temperatures during coal spontaneous combustion; S4. The calculation formula for the true critical value of CO is as follows: Where P CO (T) is the true critical value of CO on the return air side, ppm; A is the fire area of ​​the goaf, m 2 ; h is the thickness of coal left in the goaf, m; Q1 is the air leakage in the non-spontaneous combustion zone on the return air side, cm 3 / s; Q2 is the air leakage of the spontaneous combustion zone on the return air side, cm 3 / s;C CO (T) is the CO concentration on the return air side at temperature T, ppm; is the C2H4 concentration on the return air side at temperature T, ppm; is the C2H6 concentration on the return air side at temperature T, ppm; is the C3H8 concentration on the return air side at temperature T, ppm.

2. The method for calculating the real critical value of CO according to claim 1, characterized in that: In step S1, the measuring points are set on the return air side and the air inlet side of the goaf. During monitoring, the upper and lower drifts are monitored simultaneously and move synchronously with the advancement of the working face.

3. The method for calculating the real critical value of CO according to claim 1, characterized in that: In step S1, the monitoring is terminated when the measuring point enters the goaf by 240 m or the oxygen concentration drops to 8 vol.%.

4. The method for calculating the true critical value of CO according to claim 1, characterized in that: The step S2 comprises the following steps: S2-1. Based on the data monitored by the bundle tube, the trend of oxygen concentration on the air inlet side and the air return side with the burial depth is obtained; S2-2. Calculate the goaf leakage intensity and the ultimate leakage intensity on the air inlet side and the return air side; S2-3. Numerical simulation of goaf; S2-4. The three zones are divided according to the field measurement results, numerical simulation results, calculation results of air leakage intensity in goaf and calculation results of ultimate air leakage intensity in goaf.

5. The method for calculating the real critical value of CO according to claim 4, characterized in that: The calculation method of the goaf air leakage intensity and the limit air leakage intensity in step S2-2 is as follows: Air leakage intensity in goaf: In the formula, is the oxygen concentration of fresh air flow, which is 9.375×10 -6 mol / cm 3 ; The oxygen consumption rate when the coal temperature is T and the oxygen concentration is 21 vol.% is experimentally determined, mol / (s×cm 3 ), The mined area x i Air leakage intensity at , cm 3 ·(cm -2 ·s -1 ); x i+1 、x i are the distances between two points in the goaf and the working face, m; Limit oxygen concentration in goaf: Limit air leakage intensity of goaf: In the formula, is the oxygen concentration of fresh air flow, which is 21 vol.%; q0(T m ) indicates the oxygen concentration is The heat release intensity at e is the thermal conductivity of floating coal, J·s -1 cm -1 ; T m is the highest temperature in the coal body, °C; T y is the rock formation temperature, °C; T g is the air flow temperature, ℃; h is the floating coal thickness, cm; ρ g is the air flow density at the working surface, g·cm -3 ;c g is the heat capacity, J·g -1 ℃ -1 ; x is the distance between the goaf and the working face, cm; C min is the limiting oxygen concentration; is the ultimate air leakage strength, cm 3 ·(cm -2 ·s -1 ).

6. The method for calculating the true critical value of CO according to claim 4, characterized in that: The basis for dividing the three zones of the goaf in S2-4 is: Non-spontaneous combustion belt: Spontaneous combustion belt: Choking belt: In the formula, is the air leakage intensity of goaf, cm 3 ·(cm -2 ·s -1 ); is the ultimate air leakage strength, cm 3 ·(cm -2 ·s -1 ); is the oxygen concentration; C min is the limiting oxygen concentration in the goaf.

7. The method for calculating the real critical value of CO according to claim 1, characterized in that: The air leakage of the non-spontaneous combustion zone on the return air side is: The air leakage of the spontaneous combustion zone on the return air side is: Where S1 is the non-spontaneous combustion zone side area of ​​the goaf on the return air side, cm 2 ; S2 is the side area of ​​the spontaneous combustion zone on the return air side, cm 2 ; is the average value of air leakage intensity in the non-spontaneous combustion zone of the goaf on the return air side, cm 3 ·(cm -2 ·s -1 ); is the average value of air leakage intensity in the non-spontaneous combustion zone of the goaf on the return air side, cm 3 ·(cm -2 ·s -1 ); Q1 is the air leakage volume of the non-spontaneous combustion zone on the return air side, cm 3 / s; Q2 is the air leakage of the spontaneous combustion zone on the return air side, cm 3 / s.

8. Application of the CO real critical value obtained by the calculation method described in claim 1 in early warning of spontaneous combustion of coal in goaf areas.

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