Method for evaluating spontaneous combustion risk of residual coal in composite goaf of extremely close coal seam

Abstract

The invention discloses a method for evaluating spontaneous combustion risk of residual coal in a composite goaf of an extremely close coal seam, and relates to the technical field of coal mine safety testing, comprising the following steps: measuring and calculating parameters of a prepared sample; determining coal seam occurrence conditions and production conditions based on field observation; evaluation indexes are selected; based on an analytic hierarchy process and a weight method, determining the weight value and the weight value set of each evaluation index weight; and scoring and processing each evaluation index, and determining the spontaneous combustion risk level of the residual coal in the composite goaf of the extremely close coal seam. Therefore, after the weight is determined through the multi-level analysis method, the weight analysis method is used for evaluating the main factors influencing spontaneous combustion of the residual coal in the extremely close coal seam goaf, and the influence of the level of evaluation personnel on the evaluation result is reduced to the minimum.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coal mine safety testing, in particular to a method for evaluating the spontaneous combustion risk of residual coal in a composite goaf of extremely close distance coal seams. BACKGROUND

[0002] As a strategic resource indispensable to the industrialization and modernization process of China, coal will continue to bear the key role of energy security "ballast" in the current and future period. With the continuous development of coal mining technology towards high efficiency and intensification, the mining efficiency has been significantly improved, but it also brings new safety challenges. There are a large number of extremely close distance coal seam groups in the coal seam occurrence in China. Due to the small interval distance, the interval coal seam is prone to instability and collapse when mining the lower coal seam, forming a composite goaf. Such goaf not only has a wide area, complex air leakage channel, but also a larger distribution range of residual coal, thereby significantly increasing the risk of coal spontaneous combustion.

[0003] Coal spontaneous combustion is essentially a complex process of the joint action of physical and chemical factors, and its oxidation reaction mechanism has always been the focus of research in the field of coal safety mining. Generally, spontaneous combustion of residual coal is a slow oxidation process, which requires the following conditions: first, small particle size coal is more likely to spontaneously combust in a low temperature environment, second, sufficient oxygen concentration, and third, a good heat storage environment. However, these factors are often difficult to monitor and analyze in real time under actual conditions, and extreme conditions further increase the complexity of evaluation. On the other hand, some indicators affecting coal spontaneous combustion can still be measured manually. Therefore, how to effectively use existing data to accurately evaluate the spontaneous combustion risk of residual coal in the goaf of extremely close distance coal seams, so as to realize early warning and prevention, has become an important issue in current coal mine safety management. The current risk assessment of residual coal spontaneous combustion in goaf is greatly influenced by the subjective factors of evaluation experts, and the evaluation results of evaluation personnel with different experiences and levels differ greatly, which easily leads to inaccurate evaluation results. SUMMARY

[0004] The purpose of the present application is to provide a method for evaluating the spontaneous combustion risk of residual coal in a composite goaf of extremely close distance coal seams, which aims to overcome the above-mentioned problems existing in the prior art.

[0005] To achieve the purpose, the present application provides the following technical scheme:

[0006] A method for evaluating the spontaneous combustion risk of residual coal in a composite goaf of extremely close distance coal seams, characterized in that it comprises the following steps:

[0007] Step S100: measuring the parameters of the prepared sample;

[0008] Step S200: determining the coal seam occurrence conditions and production conditions based on field observation;

[0009] Step S300: selecting evaluation indexes;

[0010] Step S400: determining the weight value and weight value set of each evaluation index based on the analytic hierarchy process and weight method;

[0011] Step S500: scoring and processing each evaluation index to determine the risk grade of residual coal spontaneous combustion in the extremely close distance coal seam composite goaf.

[0012] Further, the step S100 comprises the following steps:

[0013] Step S101: crushing the residual coal samples of the upper and lower goafs and the rock samples of the interval strata collected on site, and then stacking and reorganizing them in the order of upper residual coal-interval rock-lower residual coal to prepare samples; the thickness of each reorganized layer of the sample is proportional to the actual thickness on site;

[0014] Step S201: crushing and grinding the sample, and then performing XRD diffraction test to determine the carbonization metamorphic degree of the sample, determining the sulfur content of the sample based on the Astin chart method, and calculating the oxygen consumption rate and heat release intensity of the sample based on the programmed temperature experiment and later calculation.

[0015] Further, in the step S201, the oxygen consumption rate of the sample is calculated according to formula (1), and the heat release intensity of the sample is calculated according to formula (2);

[0016]

[0017] In the formula, S is the internal cross-sectional area of the furnace body, Q is the air leakage intensity through the coal body, C0 is the oxygen concentration under fresh air flow, Ci is the oxygen concentration under actual conditions, and Zi is the oxygen concentration at different times.

[0018]

[0019] In the formula, T is the temperature of crushed coal, t is time, λ e is the thermal conductivity of loose coal body, ρ e is the density of loose coal body, c e is the heat capacity of loose coal body, ρ g is the density of air, and c g is the heat capacity of air.

[0020] Further, the step S200 comprises the following steps:

[0021] Step S201: determining the rock stratum caving degree and the geological structure of the goaf through on-site geological survey;

[0022] Step S202: calculating the maximum air leakage intensity of the goaf by measuring the rock mass temperature and air flow temperature of the goaf on site, combined with the residual coal thickness.

[0023] Step S300: selecting evaluation indexes.

[0024] Further, in the step S300, the selected evaluation indexes are as follows:

[0025] Sample spontaneous combustion tendency, including carbonization metamorphic degree, sulfur content and porosity of the sample;

[0026] Production conditions, including surrounding rock properties, surrounding rock temperature and goaf air leakage condition;

[0027] Occurrence conditions, including the degree of fragmentation of residual coal, the geological structure of the goaf, the thickness of the coal seam and the interval rock;

[0028] Sample spontaneous combustion characteristic parameters, including oxygen consumption rate, heat release intensity and residual coal thickness;

[0029] Safety management, including safety education, safety inspection and personnel quality;

[0030] Preventive measures, including roof handling, fire retardant and pressure equalization fire prevention.

[0031] Further, the step S400 includes the following steps:

[0032] Step S401: setting a weight value set for each evaluation index;

[0033] Step S402: comparing the importance of each element of the weight value set by experts, and constructing a judgment matrix.

[0034] Step S403: normalizing each column element of the judgment matrix in turn to obtain a column-normalized judgment matrix;

[0035] Step S404: adding the normalized judgment matrix by row to obtain a row vector;

[0036] Step S405: normalizing the row vector;

[0037] Step S406: calculating the maximum eigenvalue of the judgment matrix;

[0038] Step S407: consistency check; when determining the coefficients of the judgment matrix, it is required that there is consistency between the scores of the two importance comparisons; find the average random consistency index RI of the judgment matrix with order number N, obtain the consistency ratio CR, and make consistency judgment;

[0039] Step S408: through steps S402 to S407, the judgment matrix of each weight value set is checked for consistency, and finally the weight value distribution result of each evaluation index is obtained.

[0040] Further, in step S500, according to the calculated limit characteristic parameters of coal spontaneous combustion, each evaluation index is scored by experts, the score range is (0, 100); the normalized score result is recorded as Di, and the value obtained after comprehensively considering the evaluation results of multiple experts is recorded as

[0041] The risk assessment result is as follows:

[0042] When When the risk of spontaneous combustion of residual coal in the composite goaf of the extremely close distance coal seam is judged to be safe, the residual coal in the goaf has no risk of spontaneous combustion;

[0043] When When the risk of spontaneous combustion of residual coal in the composite goaf of the extremely close distance coal seam is judged to be critical, the residual coal in the goaf has a low risk of spontaneous combustion, and protective measures are needed;

[0044] When When the risk of spontaneous combustion of residual coal in the composite goaf of the extremely close distance coal seam is judged to be relatively dangerous;

[0045] When When the risk of spontaneous combustion of residual coal in the composite goaf of the extremely close distance coal seam is judged to be dangerous, and When the risk of spontaneous combustion of residual coal in the composite goaf of the extremely close distance coal seam is judged to be fatal.

[0046] Compared with the prior art, the present application has the following beneficial effects:

[0047] The risk assessment method for spontaneous combustion of residual coal in the composite goaf of the extremely close distance coal seam provided by the present application has the following remarkable advantages:

[0048] 1. Systematic and comprehensive: from sample experiments, field observations to multi-index comprehensive evaluation, a complete and scientific evaluation system is constructed, covering various influencing factors of coal spontaneous combustion.

[0049] 2. Scientific weight distribution: combined with the analytic hierarchy process and multi-source data processing technology, the rationality and objectivity of the weight of each evaluation index are ensured, and the influence of human subjective factors is significantly reduced.

[0050] 3. Strong operability: clear steps, clear indexes, and specific scoring standards make it easy for field technicians to operate and implement, and have high engineering applicability.

[0051] 4. Outstanding early warning function: through the grading determination mechanism, different risk levels can be accurately identified, and clear disposal suggestions are provided for critical and above states, realizing early warning and active prevention and control.

[0052] 5. Scalability and great potential for intelligentization: The method framework is open and easy to introduce advanced technologies such as Internet of Things, big data, artificial intelligence, etc., to further improve the accuracy and response speed of the evaluation.

[0053] In summary, the present application not only fills the gap in the field of evaluation of residual coal spontaneous combustion in close-distance composite goaf, but also embodies the characteristics of modern engineering technology of multidisciplinary intersection and intelligent integration at the methodological level, so that the influence of the level of the evaluator on the evaluation result is minimized, and the present application has high popularization and application value and market prospect. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 A simple flowchart of the present application. DETAILED DESCRIPTION

[0055] The specific embodiments of the present application will be described below with reference to the accompanying drawings. In order to fully understand the present application, many details are described below, but the present application can be implemented without these details for those skilled in the art.

[0056] In view of the deficiencies and limitations of the traditional residual coal spontaneous combustion risk evaluation method, the present application aims to seek a residual coal spontaneous combustion risk evaluation method suitable for close-distance composite goaf, which comprehensively considers six aspects of spontaneous combustion tendency, production conditions, occurrence conditions, sample spontaneous combustion limit characteristic parameters, safety management and preventive measures, and determines the weight of each aspect in evaluation through analytic hierarchy process, thereby providing a basis for evaluating the risk of residual coal spontaneous combustion in close-distance composite goaf.

[0057] As shown in Figure 1 A residual coal spontaneous combustion risk evaluation method for close-distance composite goaf, comprising the following steps:

[0058] Step S100: Parameter calculation on the prepared sample. The physical and chemical parameters (such as oxygen consumption rate and heat release intensity) of the sample are accurately measured in the laboratory to provide a scientific and reliable data basis for subsequent evaluation and reduce the uncertainty of field measurement.

[0059] In one embodiment, the above step S100 comprises the following steps:

[0060] Step S101: The residual coal samples of the upper and lower goafs and the rock samples of the interval rock layer collected on site are crushed, and then stacked and reorganized in the order of upper residual coal-interval rock-lower residual coal to prepare the sample; the thickness of each reorganized layer of the sample is proportional to the actual thickness on site.

[0061] Step S102: After the sample is crushed and ground to 325 mesh, XRD diffraction test is performed to determine the carbonization modification degree of the sample; based on the Astm card method, the sulfur content of the sample is determined; based on the programmed temperature experiment and the later calculation, the oxygen consumption rate of the sample is calculated according to formula (1), and the heat release intensity of the sample is calculated according to formula (2).

[0062]

[0063] In the formula, S is the cross-sectional area inside the furnace body; Q is the air leakage intensity through the coal body; C0 is the oxygen concentration under fresh air flow, C i is the oxygen concentration under actual conditions; Z i is the oxygen concentration at different times.

[0064]

[0065] In the formula, T is the temperature of the crushed coal; t is the time; λ e is the thermal conductivity of the loose coal body; p e is the density of the loose coal body; c e is the heat capacity of the loose coal body; p g is the density of air; c g is the heat capacity of air; z and r are the axial coordinate and radial coordinate of the loose coal body, respectively.

[0066] Step S200: Based on field observation, the occurrence conditions and production conditions of the coal seam are determined. Combined with geology and production practice, key environmental parameters such as air leakage intensity and surrounding rock temperature are obtained to ensure that the evaluation model is close to the actual working condition and enhances the field applicability of the evaluation.

[0067] In a specific implementation, the above step S200 comprises the following steps:

[0068] Step S201: Through field geological survey, the rock stratum caving degree of the composite goaf and the geological structure of the goaf are determined.

[0069] Step S202: Through field measurement of goaf rock temperature and air flow temperature, combined with residual coal thickness, the maximum air leakage intensity of the goaf is calculated according to formula (3).

[0070]

[0071] In the formula, T c is the coal temperature, since the air leakage flow in the floating coal body is small, the air flow temperature can be approximately considered as equal to the coal temperature; T y is the rock temperature, h is the residual coal thickness; when the upper layer is used, h is the upper layer residual coal thickness; when the lower layer is used, h is the lower layer residual coal thickness.

[0072] Step S300: Select the evaluation index.

[0073] In a specific implementation, step S300 selects evaluation indexes for evaluating the risk of spontaneous combustion of residual coal in the composite goaf of close-range coal seams according to the data obtained in steps S100 and S200:

[0074] ① sample spontaneous combustion tendency, including carbonization metamorphic degree, sample sulfur content and porosity;

[0075] ② production conditions, including surrounding rock properties, surrounding rock temperature and goaf air leakage condition;

[0076] ③ occurrence conditions, including residual coal fragmentation, goaf geological structure, coal seam and interval rock thickness;

[0077] ④ sample spontaneous combustion characteristic parameters, including oxygen consumption rate, heat release intensity and residual coal thickness;

[0078] ⑤ safety management, including safety education, safety inspection and personnel quality;

[0079] ⑥ preventive measures, including roof falling treatment, fire retardant fire prevention and pressure equalization fire prevention.

[0080] In the above step S300, the six categories of factors affecting coal spontaneous combustion are systematically covered, ensuring the comprehensiveness and systematicness of the evaluation dimension and avoiding omission of important indexes.

[0081] Step S400: determining the weight value set of the evaluation indexes based on the analytic hierarchy process and the weight method. The analytic hierarchy process method is used to verify the weight of each evaluation index, reduce subjective randomness, and improve the objectivity and reliability of the evaluation results.

[0082] In a specific embodiment, step S400 includes the following steps:

[0083] Step S401: setting the weight value set of each evaluation index. The first-level weight value set of the first-level evaluation indexes is γ={γ1, γ2, γ3, γ4, γ5, γ6}; wherein γ1, γ2, γ3, γ4, γ5, γ6 are sample spontaneous combustion tendency, production conditions, occurrence conditions, sample spontaneous combustion characteristic parameters, safety management and preventive measures respectively; the first-level weight value set of the second-level evaluation indexes is respectively:

[0084] ① sample spontaneous combustion tendency: γ1={γ11, γ12, γ13}; wherein γ11, γ12, γ13 are carbonization metamorphic degree, sample sulfur content and porosity respectively.

[0085] ② production conditions: γ2={γ21, γ22, γ23}; wherein γ21, γ22, γ23 are surrounding rock properties, surrounding rock temperature and goaf air leakage condition respectively.

[0086] ③ Occurrence condition: γ3={γ31, γ32, γ33}; wherein, γ31, γ32, γ33 are the broken degree of residual coal, the geological structure of goaf, and the thickness of coal seam and interval stratum, respectively.

[0087] ④ Spontaneous combustion characteristic parameter of sample: γ4={γ41, γ42, γ43}; wherein, γ41, γ42, γ43 are the oxygen consumption rate, the heat release intensity, and the residual coal thickness, respectively.

[0088] 43 respectively are the oxygen consumption rate, the heat release intensity, and the residual coal thickness.

[0089] ⑤ Safety management: γ5={γ51, γ52, γ53}; wherein, γ51, γ52, γ53 are the safety education, the safety inspection, and the personnel quality, respectively.

[0090] ⑥ Preventive measures: γ6={γ61, γ62, γ63}; wherein, γ61, γ62, γ63 are the roof fall treatment, the fire prevention by inhibitor, and the pressure equalization fire prevention, respectively.

[0091] Step S402: the elements of the first weight value set are compared in importance two by two by experts, and an n×n judgment matrix is constructed.

[0092] Step S403: the elements of each column of the judgment matrix are normalized in turn according to formula (4), and a judgment matrix normalized by column is obtained.

[0093]

[0094] Step S404: the normalized judgment matrix is added by row according to formula (5), and a row vector is obtained.

[0095]

[0096] Step S405: the row vector is normalized according to formula (6):

[0097]

[0098] Step S406: the maximum eigenvalue of the judgment matrix is calculated according to formula (7):

[0099]

[0100] Step S407: consistency check is performed; when the coefficients of the judgment matrix are determined, consistency between the scores of the importance comparison two by two is required:

[0101]

[0102] The average random consistency index RI of the judgment matrix of order N is calculated, and a consistency ratio CR is obtained according to the consistency index RI and a consistency parameter CI, and a consistency judgment is performed. The consistency ratio CR is calculated according to formula (9):

[0103]

[0104] Step S408: The judgment matrix of each secondary weight value set is subjected to pairwise consistency test through steps S402 to S407, and finally the weight value distribution result of the primary and secondary evaluation indexes is obtained.

[0105] Step S500: Scoring and processing each evaluation index, and scoring each evaluation index by an expert to determine the risk grade of the extremely close coal seam composite goaf residual coal spontaneous combustion.

[0106] In a specific embodiment, step S500 comprises the following steps:

[0107] Step S501: Scoring each evaluation index by an expert according to the calculated limit characteristic parameters of coal spontaneous combustion, and the scoring range is (0, 100); the scoring result is normalized and recorded as Di, and the value obtained after considering the evaluation results of multiple experts is recorded as

[0108] The risk assessment result is as follows:

[0109] When The risk of the extremely close coal seam composite goaf residual coal spontaneous combustion is determined to be safe, at which time the goaf residual coal has no spontaneous combustion risk.

[0110] When The risk of the extremely close coal seam composite goaf residual coal spontaneous combustion is determined to be critical, at which time the goaf residual coal has a low spontaneous combustion risk and needs to be protected.

[0111] When The risk of the extremely close coal seam composite goaf residual coal spontaneous combustion is determined to be relatively dangerous;

[0112] When The risk of the extremely close coal seam composite goaf residual coal spontaneous combustion is determined to be dangerous, and The risk of the extremely close coal seam composite goaf residual coal spontaneous combustion is determined to be fatal.

[0113] The above step S500 obtains the risk grade by multiple expert scoring and normalization processing, which is strong in operability, intuitive in result, and convenient for on-site safety management decision-making.

[0114] Embodiment 1:

[0115] In order to better illustrate the present application, the following is a detailed description of a certain mine composite goaf. The specific steps of this embodiment 1 are as follows:

[0116] (1) The parameters of the prepared sample are measured.

[0117] (1.1) The composite goaf residual coal and the interval rock layer are sampled in the field, and the average thickness of the upper residual coal is determined to be 0.8 m, the average thickness of the interval rock layer is determined to be 1.2 m, and the average thickness of the lower residual coal is determined to be 1 m. The residual coal samples and rock samples of the interval rock layer are crushed, and then stacked and reorganized in the order of upper residual coal-interval rock-lower residual coal. The sample is prepared; in the sample, the thickness of the upper residual coal is 26.6 mm, the thickness of the interval rock is 40 mm, and the thickness of the lower residual coal is 33.4 mm.

[0118] (1.2) After the sample is crushed and ground to 325 mesh, XRD diffraction test is performed to determine the carbonization metamorphic degree of the sample; based on the Astic chart method, the sulfur content of the sample is determined; based on the programmed temperature experiment and the later calculation, the oxygen consumption rate of the sample is calculated according to the above formula (1), and the heat release intensity of the sample is calculated according to formula (2).

[0119]

[0120] Wherein, S is the cross-sectional area inside the furnace body; Q is the air leakage intensity through the coal body; C0 is the oxygen concentration under fresh air flow, Ci is the oxygen concentration under actual conditions; Zi is the oxygen concentration at different times.

[0121]

[0122] In the formula: T is the temperature of the crushed coal; t is the time; λ e is the thermal conductivity of the loose coal body; p e is the density of the loose coal body; c e is the heat capacity of the loose coal body; p g is the density of air; c g is the heat capacity of air; z and r are the axial coordinate and radial coordinate of the loose coal body, respectively.

[0123] The calculation results are as follows:

[0124]

[0125] (2) Based on the field observation, the coal seam occurrence conditions and production conditions are determined.

[0126] (2.1) Through field geological survey, the temperature of the surrounding rock of the composite goaf and the geological structure of the goaf are determined.

[0127] Wherein, the temperature of the surrounding rock of the goaf is measured as 41℃; the coal seam is located in a synclinal basin, and the mining conditions are good.

[0128] (2.2) By measuring the temperature of the rock mass and the air flow in the goaf, and combining with the thickness of the residual coal, the maximum air leakage intensity of the goaf is calculated according to formula (3).

[0129]

[0130] In the formula, Tc is the temperature of the coal body; and Ty is the temperature of the rock mass.

[0131] (3) Selecting the evaluation indexes for the risk assessment of the spontaneous combustion of the residual coal in the composite goaf of the close-distance coal seams:

[0132] ① The spontaneous combustion tendency of the sample, including the carbonization metamorphic degree, the sulfur content and the porosity of the sample;

[0133] ② The production conditions, including the properties of the surrounding rock, the temperature of the surrounding rock and the air leakage condition of the goaf;

[0134] ③ The occurrence conditions, including the fragmentation degree of the residual coal, the geological structure of the goaf, the thickness of the coal seam and the interval rock;

[0135] ④ The spontaneous combustion characteristic parameters of the sample, including the oxygen consumption rate, the heat release intensity and the thickness of the residual coal;

[0136] ⑤ The safety management, including the safety education, the safety inspection and the personnel quality;

[0137] ⑥ The preventive measures, including the roof fall treatment, the fire prevention by the inhibitor and the fire prevention by the pressure equalization;

[0138] (4) The weight value set of the evaluation indexes given by the experts is verified for consistency by using the analytic hierarchy process, including the following steps:

[0139] (4.1) Setting the weight value set of the evaluation indexes, the first-level weight value set u of the first-level evaluation indexes is {u1, u2, u3, u4, u5, u6}, and the second-level weight value set of the second-level evaluation indexes contained in each first-level evaluation index is:

[0140] ① The spontaneous combustion tendency of the sample: u1={u11, u12, u13}; wherein u11, u12 and u13 are respectively the carbonization metamorphic degree, the sulfur content and the porosity of the sample.

[0141] ② The production conditions: u2={u21, u22, u23}; wherein u21, u22 and u23 are respectively the properties of the surrounding rock, the temperature of the surrounding rock and the air leakage condition of the goaf

[0142] ③ Occurrence conditions: u3 = {u31, u32, u33}; where u31, u32, and u33 are the degree of fragmentation of the residual coal, the geological structure of the goaf, and the thickness of the coal seam and the interstitial strata, respectively.

[0143] ④ The spontaneous combustion characteristic parameters of the sample: u4={u41,u42,u43}; where u41, u42, and u43 are the oxygen consumption rate, heat release intensity, and residual coal thickness, respectively.

[0144] ⑤ Safety Management: u5 = {u51, u52, u53}; where u51, u52, and u53 are safety education, safety inspection, and personnel quality, respectively.

[0145] ⑥ Preventive measures: u6 = {u61, u62, u63}; where u61, u62, and u63 are respectively roof fall treatment, fire inhibitor fire prevention, and pressure equalization fire prevention.

[0146] (4.2) Experts conduct pairwise importance comparisons of each element in the first-level weight value set, constructing an n×n judgment matrix. The following is a judgment matrix made by one expert:

[0147]

[0148] (4.3) Normalize the elements of each column in turn to obtain the column-normalized matrix:

[0149]

[0150] The row vector is obtained by summing the normalized judgment matrix row by row.

[0151] (0.587 0.345 1.584 1.946 0.648 0.891) T

[0152] Normalize the row vectors:

[0153] (0.098 0.057 0.264 0.324 0.108 0.149) T

[0154] The largest eigenvalue of the matrix is ​​calculated to be λmax = 6.37.

[0155] (4.4) Perform a consistency test. When determining the coefficients of the judgment matrix, consistency is required between the scores of pairwise importance comparisons.

[0156]

[0157] The average random consistency index RI of the judgment matrix of order N is used to obtain the consistency ratio CR; and a consistency judgment is made.

[0158]

[0159] (4.5) Similarly, by steps (4.2) to step (4.4), the consistency of each secondary weight value set is verified by using the analytic hierarchy process; finally, the weight value distribution results of the primary and secondary evaluation indexes are obtained, as shown in Table 1.

[0160] Table 1 Weight value distribution of evaluation indexes

[0161]

[0162] (5) Based on the score of each evaluation index, the risk grade of residual coal spontaneous combustion in the extremely close distance coal seam composite goaf is determined. The specific steps are as follows:

[0163] (5.1) Based on the data obtained by experiments and field investigation, each evaluation index is scored by experts, and the score range is (0, 100). Table 2 is the score results of a certain expert.

[0164] Table 2 Evaluation results

[0165] Index Score Index Score Degree of carbonization V1 78 Oxygen consumption rate 87 Sulfur content V2 83 Heat release intensity 85 Porosity V3 85 Thickness of residual coal 78 Surrounding rock temperature V3 77 Safety education 86 Air leakage condition V4 79 Safety inspection 80 Surrounding rock properties V5 86 Personnel quality 85 Degree of fragmentation of residual coal V6 83 Pressure equalization fire prevention 81 Geological structure V7 78 Roof treatment 85 Thickness of coal seam V8 91 Inhibitor fire prevention 83

[0166] ②The score results are normalized and recorded as Di, and the values obtained after considering the evaluation results of multiple experts are recorded as

[0167] After processing the evaluation results of multiple experts, the final evaluation results are obtained That is, the residual coal spontaneous combustion risk of the composite goaf of the mine is critical, and there is a risk of residual coal spontaneous combustion, which needs to be improved by certain safety measures.

[0168] The above is only a specific embodiment of the present application, but the design concept of the present application is not limited thereto, and any non-essential modification of the present application using this concept shall be regarded as an act of infringing the protection scope of the present application.

Claims

1. A method for evaluating the spontaneous combustion risk of residual coal in a combined goaf of close distance coal seams, characterized in that, The method comprises the following steps: Step S100: parameter measurement on the prepared sample; Step S200: based on field observation, determine the occurrence conditions and production conditions of the coal seam; Step S300: select evaluation indexes; Step S400: based on the analytic hierarchy process and the weight method, determine the weight value set of the evaluation indexes; Step S500: score and process each evaluation index, and determine the risk grade of the residual coal spontaneous combustion in the extremely close distance composite goaf.

2. The method for evaluating the spontaneous combustion risk of residual coal in the compound goaf of close distance coal seams according to claim 1, characterized in that, The step S100 comprises the following steps: Step S101: the residual coal samples of the upper and lower goafs and the rock samples of the interval strata collected in the field are crushed, and then stacked and reorganized in the order of upper residual coal-interval rock-lower residual coal to prepare the sample; the thickness of each reorganization layer of the sample is proportional to the actual thickness in the field; Step S201: after crushing and grinding the sample, XRD diffraction test is performed to determine the carbonization metamorphic degree of the sample, and based on the Astic chart method, the sulfur content of the sample is determined; based on the programmed temperature experiment and the later calculation, the oxygen consumption rate and the heat release intensity of the sample are calculated.

3. The method for evaluating the spontaneous combustion risk of residual coal in the compound goaf of close distance coal seams according to claim 1, characterized in that, In the step S201, the oxygen consumption rate of the sample is calculated according to formula (1), and the heat release intensity of the sample is calculated according to formula (2); In the formula, S is the internal cross-sectional area of the furnace body, Q is the air leakage intensity through the coal body, C0 is the oxygen concentration under fresh air flow, Ci is the oxygen concentration under actual conditions, and Zi is the oxygen concentration at different times; where: T = coal temperature; t = time; λ e —thermal conductivity of the loose coal mass; p e —density of the loose coal mass; c e —heat capacity of the loose coal mass; p g —density of air; c g —heat capacity of air; z and r are the axial and radial coordinates of the loose coal mass, respectively.

4. The risk assessment method for spontaneous combustion of residual coal in the compound goaf of close distance coal seams according to claim 1, 2 or 3, characterized in that, The step S200 comprises the following steps: Step S201: through field geological survey, determine the rock stratum caving degree of the composite goaf and the geological structure of the goaf; Step S202: through field measurement of the goaf rock mass temperature and the air flow temperature, combined with the residual coal thickness, calculate the maximum air leakage intensity of the goaf; Step S300: select evaluation indexes.

5. The method for evaluating the spontaneous combustion risk of residual coal in the compound goaf of close distance coal seams according to claim 1, characterized in that, In the step S300, the selected evaluation indexes are as follows: Sample spontaneous combustion tendency, including carbonization metamorphic degree, sulfur content and porosity of the sample; Production conditions, including surrounding rock properties, surrounding rock temperature and goaf air leakage condition; Occurrence conditions, including the crushing degree of residual coal, the geological structure of the goaf, the thickness of the coal seam and the interval strata; Sample spontaneous combustion characteristic parameters, including oxygen consumption rate, heat release intensity and residual coal thickness; Safety management, including safety education, safety inspection and personnel quality; Preventive measures, including roof falling treatment, fire retardant and pressure equalization fire prevention.

6. The risk assessment method for spontaneous combustion of residual coal in the compound goaf of close distance coal seams according to claim 1 or 5, characterized in that, The step S400 comprises the following steps: Step S401: set the weight value set of each evaluation index; Step S402: by experts, compare the importance of each element of the weight value set two by two to construct a judgment matrix. Step S403: normalize each column element of the judgment matrix in turn to obtain the normalized judgment matrix by column; Step S404: add the normalized judgment matrix by row to obtain a row vector; Step S405: normalize the row vector; Step S406: calculate the maximum eigenvalue of the judgment matrix; Step S407: perform consistency check; When determining the coefficients of the judgment matrix, consistency is required between the scores of the two-by-two importance comparison. The average random consistency index RI of the judgment matrix with order N is obtained, a consistency ratio CR is derived, and a consistency judgment is performed. Step S408: Through steps S402 to S407, the judgment matrix of each weight value set is subjected to pairwise consistency test, and finally the weight value distribution result of each evaluation index is obtained.

7. The method for evaluating the spontaneous combustion risk of residual coal in the compound goaf of close distance coal seams according to claim 1, characterized in that, In step S500, according to the limit characteristic parameters of coal spontaneous combustion calculated, each evaluation index is scored by experts, and the score range is (0, 100); the score result is normalized and recorded as Di, and the value obtained after considering the evaluation results of multiple experts is recorded as The risk assessment results are as follows: When If the risk of spontaneous combustion of residual coal in the compound goaf of the close distance coal seams is determined to be safe, the residual coal in the goaf has no risk of spontaneous combustion. When The risk of spontaneous combustion of residual coal in the compound goaf of the close-distance coal seams is critical, at this time, the residual coal in the goaf has a low risk of spontaneous combustion, and protective measures are needed. When The risk of spontaneous combustion of residual coal in the compound goaf of the close-distance coal seams is determined as relatively dangerous. When The risk of spontaneous combustion of residual coal in the compound goaf of the close-distance coal seams is determined as dangerous When The risk of spontaneous combustion of residual coal in the extremely close distance coal seam composite goaf is fatal.

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