Method for calculating gas concentration distribution of gob under Y-shaped ventilation of gob-side entry retaining working face

Abstract

The invention discloses a goaf gas concentration distribution calculation method under gob-side entry retaining working face Y-shaped ventilation. It is assumed that flowing of multi-element gas in a goaf meets the Darcy law; according to actual measurement results of a large number of mine rock stratum sinkage, a goaf roof rock stratum sinkage rule approximates to a negative exponential function, and it is easy to deduce that the height compression amount of a caving zone also approximates to meet the negative exponential function; a gas flow control equation; a gas convection diffusion equation; according to the characteristics of goaf gas source release, goaf gas emission mainly comes from goaf float coal gas desorption, gas released by upper and lower adjacent pressure relief coal rock layers affected by mining, and old goaf gas emission along a certain local channel; according to the goaf geometric model and the boundary condition, the goaf geometric model is established according to the collected working face condition, working face ventilation parameters and goaf gas emission quantity parameters; the problem that corner gas on the working face exceeds the limit can be effectively solved.

Description

TECHNICAL FIELD

[0001] The application relates to a kind of along empty lane working face ventilation calculation method, in particular to a kind of along empty lane working face Y type ventilation lower goaf gas concentration distribution calculation method, belongs to the technical field of mine ventilation. BACKGROUND

[0002] Along empty lane is a kind of coal mining process, by retaining the roadway on one side of the goaf as the next working face air intake lane or return air lane without coal pillar mining technology. This technology can effectively improve the coal recovery rate, reduce the roadway drivage rate, and improve the tense situation of mine mining replacement.

[0003] At present, U type ventilation is generally adopted, and the U type ventilation system is simple, the ventilation path is short, and the ventilation resistance is small, and the disadvantages are as follows:

[0004] The problem of gas accumulation is prominent, in the U type ventilation system, the upper corner of the working face is the convergence of the goaf gas flowing into the working face, and the gas is easy to accumulate here. Since the gas density is smaller than that of air, it will gather in the upper part of the upper corner, resulting in a significant increase in gas concentration; the gas in the goaf will flow into the upper corner with the air flow, but due to the slow wind speed in this area, the gas is difficult to be carried away in time, and a vortex area is easily formed, further aggravating the gas accumulation.

[0005] The ventilation stability is poor, the air flow stability of the U type ventilation system is poor, the ventilation path is single, and once the ventilation resistance changes or local air leakage occurs, the air flow is easy to be disordered, affecting the ventilation effect.

[0006] The goaf air leakage risk is high, the goaf air leakage amount is large, and the high concentration gas in the goaf is easy to enter the working face, resulting in an increase in gas concentration and an increase in gas control difficulty; air leakage may also cause the oxidation and spontaneous combustion of floating coal in the goaf, especially in high-sulfur and high-ash coal seams, the risk of spontaneous combustion is higher.

[0007] The gas control is difficult, the U type ventilation system cannot fundamentally solve the problem of gas overlimit and gas accumulation in the upper corner, and it is difficult to effectively control the gas concentration by relying on ventilation dilution.

[0008] The consequences are as follows:

[0009] The risk of gas overlimit increases, the gas accumulation in the upper corner may cause the gas concentration to exceed the safety threshold (such as 1%), or even reach the dangerous concentration (5% to 16%) of gas explosion, which seriously threatens the safety production of the working face; gas overlimit may cause the working face to stop production and rectification, affecting the production progress.

[0010] The ventilation system fails, and the poor ventilation stability may cause the air flow to be disordered, and even the air flow to be short-circuited, so that the effective ventilation volume of the working face is insufficient, further aggravating the gas accumulation.

[0011] The coal spontaneous combustion risk rises, and the goaf air leakage can cause the residual coal oxidation and spontaneous combustion, once the spontaneous combustion occurs, not only the coal resources will be burned, but also the gas explosion can be caused.

[0012] Resource waste and cost increase, due to the difficulty of gas control, it can be necessary to increase the ventilation equipment, gas extraction system and the like, resulting in the increase of production cost. SUMMARY

[0013] The purpose of the present application is to provide a kind of gob gas concentration distribution calculation method under Y type ventilation along gob roadway working face, under Y type ventilation, gob gas is mainly concentrated in the rear side close to return airway, will not surge into working face, can effectively solve the problem of gas overrun in upper corner of working face.

[0014] In order to achieve the above purpose, the present application provides a kind of gob gas concentration distribution calculation method under Y type ventilation along gob roadway working face, comprising the following steps:

[0015] S1, basic assumption

[0016] Assume that the flow of multivariate gas in the goaf satisfies Darcy's law; The height of the overburden coal and rock falling zone caused by coal seam excavation is much smaller than the length and width of the goaf, and the vertical air leakage velocity between the goaf layers is very small, so the goaf is regarded as a two-dimensional heterogeneous porous medium flow field;

[0017] S2, dynamic evolution of goaf permeability

[0018] According to a large number of measured results of mine strata subsidence, the subsidence law of goaf roof strata is approximately symbolized from negative exponential function, so it is easy to deduce that the compression amount of falling zone height also approximately satisfies negative exponential function; Considering the "O" type ring effect of goaf falling compaction, for any shape of goaf, specifically relative to a boundary j, the single direction of the broken expansion coefficient satisfies:

[0019] K P (x,y)=K P,min +(K P,max -K P,min )·exp{-a1d1·[1-exp(ξ1·a0d0)]} (1)

[0020] In the formula: K p (x,y) is the broken expansion coefficient of goaf falling coal and rock mass;

[0021] J represents the boundary;

[0022] K p·j is the broken expansion coefficient of falling coal and rock mass corresponding to boundary j;

[0023] K p·max is the initial broken expansion coefficient;

[0024] K p·min is the dilatancy coefficient of the caving coal and rock mass;

[0025] a0 and a1 are the decay rates of the distance to the solid wall and the working face, respectively;

[0026] d0 and d1 are the distances from the point (x, y) to the solid wall and the working face, respectively;

[0027] ξ1 is the adjustment number for controlling the distribution shape of the “O” ring model;

[0028] S3, the height H and the porosity n of the caving goaf are respectively expressed as a function of the dilatancy coefficient:

[0029]

[0030] In the formula: H is the caving height of the goaf;

[0031] n is the porosity of the goaf;

[0032] M is the working face mining height;

[0033] The relationship between the permeability of the goaf porous medium and the porosity n of the goaf is expressed by the Blake-Kozeny equation:

[0034]

[0035] In the formula: d p is the particle diameter of the goaf porous medium;

[0036] S4, gas flow control equation

[0037] Considering that the dynamic change of the height of the caving coal and rock mass under the continuous advancement of the working face is an important constraint on the flow field of the goaf, the mass conservation equation of the gas flow in the goaf under two-dimensional steady state is obtained:

[0038] ▽·(H·v g )=Q s (5)

[0039] In the formula: v g is the velocity vector of the mixed gas in the goaf;

[0040] Q s is the source term of the gas;

[0041] The Darcy law is used to describe the flow of the gas in the goaf porous medium:

[0042]

[0043] In the formula: p is the pressure of the mixed gas in the goaf;

[0044] μ is the dynamic viscosity coefficient of the mixed gas in the goaf;

[0045] ρ g is the mixed gas density in the goaf;

[0046] Substituting formula (6) into formula (5), the control equation of gas flow in the goaf is obtained:

[0047]

[0048] S5. Gas Convection Diffusion Equation

[0049] The gas flow in the goaf satisfies the convection-diffusion equation. Substituting the gas velocity calculated from the gas flow control equation into the convection-diffusion equation, the gas concentration distribution law in the goaf is obtained as follows:

[0050]

[0051] Where: is the gas concentration;

[0052] is the gas sink in the goaf;

[0053] c is the concentration of the mixed gas components, c = p / RT g ;

[0054] R is the gas constant;

[0055] T g is the gas temperature in the goaf;

[0056] t is time;

[0057] is the diffusion coefficient tensor of gas, expressed as:

[0058]

[0059] Where: ij is the Kronecker symbol;

[0060] v i is the component of the gas flow velocity along the x, y, and z axes, and the component in the x and y directions;

[0061] α L and α T are the longitudinal and transverse diffusion of the gas, respectively;

[0062] τ is the tortuosity of the porous medium;

[0063] D a is the molecular diffusion coefficient of gas;

[0064] Gas emission per unit volume per unit time is expressed as:

[0065]

[0066] wherein: is the cumulative release intensity of gas per unit area in the goaf;

[0067] S6, according to the release characteristics of the goaf gas source, the goaf gas emission mainly comes from the desorption of the float coal gas in the goaf, the released gas from the upper and lower adjacent pressure relief coal rock layers affected by mining, and the goaf gas emission along a certain local channel, so the cumulative release intensity of gas per unit area in the goaf at any point in the goaf under the continuous advancing of the working face is is expressed as:

[0068]

[0069] wherein: x0 is the initial position coordinate of the working face;

[0070] u is the advancing speed of the working face;

[0071] t is the mining time;

[0072] w0 is the emission intensity of the uniform and constant stable gas source in the goaf;

[0073] w1 is the initial emission intensity of the residual coal gas source in the coal seam and the gas source in the upper pressure relief coal rock layer;

[0074] λ is the gas release decay coefficient;

[0075] S7, the geometric model of the goaf and the boundary conditions

[0076] According to the collected working face conditions, the working face ventilation parameters and the goaf gas emission parameters, the geometric model of the goaf is established, and the flow field calculation parameters and the boundary conditions are shown in Table 1 and Table 2, wherein p0 is the upper corner pressure of the working face, L is the length of the working face, R and R1 are the ventilation resistances of the working face and the roadway respectively, Q is the main air volume, and Q1 is the air volume in the roadway.

[0077] The initial and boundary conditions of the model in Table 1 in step S7 of the application are:

[0078]

[0079] The numerical simulation parameters in Table 2 in step S7 of the application are:

[0080]

[0081]

[0082] Compared with the prior art, the gas of the application is mainly concentrated on the side close to the air return roadway at the rear of the goaf, and will not flow into the working face, and this distribution feature can effectively avoid the accumulation of gas in the upper corner of the working face and reduce the risk of gas overrun.

[0083] The permeability distribution under Y-type ventilation: the middle part is compacted, the permeability is small, and the permeability around is large, and this distribution form is helpful for the centralized management and extraction of gas. BRIEF DESCRIPTION OF DRAWINGS

[0084] Figure 1 The geometric model of the goaf under Y-type ventilation of the application;

[0085] Figure 2 The goaf permeability, gas pressure and gas concentration distribution under different advancing distances of the application;

[0086] Figure 3 The gas concentration distribution of the goaf under Y-type ventilation and U-type ventilation of the application. DETAILED DESCRIPTION

[0087] The application will be further described below in combination with the drawings.

[0088] A goaf gas concentration distribution calculation method under Y-type ventilation of a gob-side entry retaining working face, comprising the following steps:

[0089] S1, basic assumption

[0090] It is assumed that the flow of multi-component gas in the goaf satisfies Darcy's law; under general conditions, the height of the caving zone caused by the excavation of the coal seam is much smaller than the length and width of the goaf, and the vertical leakage velocity of the goaf interlayer is very small, so the goaf is regarded as a two-dimensional heterogeneous porous medium flow field here;

[0091] S2, dynamic evolution of goaf permeability

[0092] According to a large number of measured results of mine strata subsidence, the subsidence law of the goaf roof strata approximately satisfies the negative exponential function, so it is easy to deduce that the compression amount of the caving zone height also approximately satisfies the negative exponential function; here, the "O" ring effect of the goaf caving compaction is considered, and for any shape of goaf, the dilatancy coefficient in a single direction relative to a certain boundary j satisfies:

[0093] K P (x,y)=K P,min +(K P,max -K P,min )·exp{-a1d1·[1-exp(ξ1·a0d0)]} (1)

[0094] In the formula: K p(x, y) is the dilatancy coefficient of the caving coal and rock mass;

[0095] j represents the boundary;

[0096] K p·j is the dilatancy coefficient of the caving coal and rock mass at the corresponding boundary j;

[0097] K p·max is the initial dilatancy coefficient;

[0098] K p·min is the compaction dilatancy coefficient;

[0099] a0 and a1 are the decay rates of the caving coal and rock mass relative to the distance to the solid wall and the working face, which is related to the physical and mechanical properties of the caving coal and rock mass, the geological characteristics of the rock stratum, the mine pressure load, and the duration after breaking, and the value can be obtained through mine pressure observation;

[0100] d0 and d1 are the distances from the point (x, y) to the solid wall and the working face, respectively;

[0101] ξ1 is an adjustment number that controls the distribution form of the "O" ring model;

[0102] S3, the height H and the porosity n of the caving goaf can be represented as functions of the dilatancy coefficient, respectively:

[0103]

[0104] In the formula: H is the caving height of the goaf;

[0105] n is the porosity of the goaf;

[0106] M is the working face mining height;

[0107] The relationship between the permeability of the goaf porous medium and the porosity n of the goaf can be represented by the Blake-Kozeny equation:

[0108]

[0109] In the formula: d p is the particle diameter of the goaf porous medium;

[0110] S4, gas flow control equation

[0111] Considering that the dynamic change of the height of the caving coal and rock mass under the continuous advancement of the working face is an important constraint on the flow field of the goaf, the mass conservation equation of the gas flow in the goaf under two-dimensional steady state can be obtained:

[0112] ▽·(H·v g )=Q s (5)

[0113] wherein: v g is the velocity vector of the mixed gas in the goaf;

[0114] Q s is the source (sink) term of the gas;

[0115] The Darcy's law is used to describe the flow of the gas in the porous medium of the goaf:

[0116]

[0117] wherein: p is the pressure of the mixed gas in the goaf;

[0118] μ is the dynamic viscosity coefficient of the mixed gas in the goaf;

[0119] ρ g is the density of the mixed gas in the goaf;

[0120] The control equation of the gas flow in the goaf is obtained by substituting formula (6) into formula (5):

[0121]

[0122] S5, gas convection-diffusion equation

[0123] The gas flow in the goaf satisfies the convection-diffusion equation. The gas flow rate calculated from the gas flow control equation is substituted into the convection-diffusion equation, and the gas concentration distribution law in the goaf is obtained as follows:

[0124]

[0125] wherein: is the gas concentration;

[0126] is the sink-source term of the gas in the goaf;

[0127] c is the concentration of the mixed gas component, c = p / RT g ;

[0128] R is the gas constant;

[0129] T g is the temperature of the gas in the goaf;

[0130] t is time;

[0131] is the diffusion coefficient tensor of the gas, which can be expressed as:

[0132]

[0133] wherein: ξ ij is the kronecker symbol;

[0134] v i is the component of the gas flow velocity along the x, y, and z axes, and the component in the x and y directions;

[0135] α L and α T are the longitudinal and transverse diffusion of the gas, respectively;

[0136] τ is the tortuosity of the porous medium;

[0137] D a is the molecular diffusion coefficient of gas;

[0138] Gas emission per unit volume and time It can be expressed as:

[0139]

[0140] Where: is the cumulative gas release intensity per unit area of ​​the goaf;

[0141] S6. According to the characteristics of gas source release in goaf, gas outburst in goaf mainly comes from gas desorption of floating coal in goaf, gas released from upper and lower adjacent unloaded coal and rock layers affected by mining, and gas outburst from old goaf along a certain local channel. Therefore, the cumulative gas release intensity per unit area of ​​goaf at any point in goaf under continuous advancement of working face is: It can be expressed as:

[0142]

[0143] Where: x0 is the initial position coordinate of the working surface;

[0144] u is the working face advancement speed;

[0145] t is the mining time;

[0146] w0 is the uniform and stable gas source emission intensity in the goaf;

[0147] w1 is the initial outburst intensity of the gas source of the coal seam and the gas source of the upper unloaded coal and rock layer;

[0148] λ is the gas release attenuation coefficient;

[0149] S7. Geometric model and boundary conditions of goaf

[0150] According to the collected working face conditions, working face ventilation parameters, goaf gas emission and other parameters, a geometric model of the goaf is established. Figure 1As shown, the flow field calculation parameters and boundary conditions are shown in Table 1 and Table 2 respectively. In Table 1, p0 is the corner pressure of the working surface, L is the length of the working surface, R and R1 are the ventilation resistance of the working surface and the remaining lane respectively, Q is the main air volume, and Q1 is the air volume in the remaining lane.

[0151] The model initial and boundary conditions in Table 1 in step S7 are:

[0152]

[0153]

[0154] The numerical simulation parameters in Table 2 in step S7 are:

[0155] Parameter K P,max ]]> K P,min ]]> [a0] [a1] ​ μ Value 1.4 1.15 0.068 0.0368 0.233 1.84 x 10 -5 ]]> Unit —— —— m -1 ]]> m -1 ]]> —— N s / m 2 ]] Parameter <![CDATA[D a ]]> Q Q1 R [p0] L Value 2 x 10 -5 ]]> 2000 2800 5 x 10 -5 ]]> 0 230 Unit m 2 / s]]> m 3 / min]]> m 3 / min]]> N·s 2 / m 9 ]]> Pa m Parameter L ]]> ​ T ]]> ​ d p ]]> w0 w1 λ Value 5 1.5 0.04 4 8 0.076 Unit m m m mol / (m 2 ·h)]]> mol / (m 2 ·h)]]> d -1 ]]>

[0156] Figure 2 The figure shows the distribution of permeability, gas pressure and gas concentration in the goaf when the Y-type ventilation working face advances 360m, 540m and 720m. Figure 2 The permeability distribution conforms to an "O"-shaped ring, with low permeability due to compaction in the center and high permeability due to support from the coal wall. The pressure distribution diagram shows that the pressure on the air inlet side is higher, and the gas concentration is lowest at the rear of the return air lane. Therefore, due to the pressure differential, gas from the goaf may flow into the return air lane, causing the gas concentration in the return air lane to exceed the limit. The gas concentration distribution diagram shows that gas is mainly concentrated at the rear of the goaf, near the return air lane. After the working face advances 720 meters, the gas concentration in the upper corner of the goaf reaches 34.5%.

[0157] like Figure 3 Shown are the gas concentration distribution diagrams of the goaf of "U" type and "Y" type ventilation working faces under the same conditions.

[0158] Depend on Figure 3 It can be seen that in the case of a "U"-shaped ventilation working face, a large amount of goaf gas is carried to the corner of the working face by the wind flow, and the amount of gas flowing into the working face is 15.6m3 / min, which can easily lead to excessive gas in the corner of the working face. The air pressure of the "Y"-shaped ventilation working face is higher than the air pressure of the return air lane. Therefore, the gas in the goaf is concentrated at the rear of the goaf near the return air lane and will not flow into the working face, which can effectively solve the problem of excessive gas in the corner of the working face. However, due to the inevitable air leakage of the closed wall along the goaf, the gas in the goaf may enter the return air lane. Therefore, it is necessary to insert a pipe in the return air lane to extract the gas in the goaf to prevent the gas in the goaf from entering the return air lane and causing the gas concentration in the return air lane to exceed the limit.

[0159] The present application studies the gas distribution law in goaf under Y-type ventilation mode, and compares and analyzes with U-type ventilation. The results show that under Y-type ventilation mode, the gas in goaf is mainly concentrated in the rear side close to the return airway, and will not surge into the working face, effectively solving the problem of gas overrun in the upper corner of the working face. Through numerical simulation, the gas distribution characteristics of Y-type ventilation under different advancing distances are determined, which provides a scientific basis for optimizing the ventilation system design. The main research contents are as follows:

[0160] (1) Gas distribution law in goaf under Y-type ventilation mode

[0161] Gas distribution characteristics: The gas is mainly concentrated in the rear side close to the return airway in goaf, and will not surge into the working face, which effectively avoids the accumulation of gas in the upper corner of the working face and reduces the risk of gas overrun.

[0162] Permeability distribution: The middle part is compacted, the permeability is small, and the permeability around is large, which is helpful for the centralized management and extraction of gas.

[0163] (2) Comparative analysis of U-type ventilation

[0164] Gas concentration distribution: Y-type ventilation effectively solves the problem of gas overrun in the upper corner of the working face, compared with U-type ventilation, under which the gas is more likely to surge into the working face, resulting in an increased risk of gas overrun.

[0165] Ventilation system optimization: Through numerical simulation, the gas distribution characteristics of Y-type ventilation under different advancing distances are determined, which provides a basis for the design of ventilation system.

Claims

1. A method for calculating gas concentration distribution in goaf under Y-type ventilation in goaf-side entry retaining working face, characterized in that: The following steps are involved: S1. Basic assumptions Assuming that the flow of multi-element gases in the goaf satisfies Darcy's law; the height of the overlying coal and rock caving zone caused by coal seam excavation is much smaller than the length and width of the goaf, and the component velocity of vertical air leakage between layers in the goaf is very small, the goaf is regarded as a two-dimensional heterogeneous porous medium flow field; S2. Dynamic evolution of permeability in goaf According to the measured results of rock strata subsidence in a large number of mines, the subsidence law of the roof rock strata in the goaf is approximately in accordance with the negative exponential function. It is easy to infer that the height compression of the caving zone also approximately satisfies the negative exponential function. Considering the "O" ring effect of caving and compaction in the goaf, for a goaf of any shape, specifically relative to a certain boundary j, its single-direction expansion coefficient satisfies: K P (x,y)=K P,min +(K P,max -K P,min )·exp{-a1d1·[1-exp(ξ1·a0d0)]} (1) Where: K p (x,y) is the expansion coefficient of coal and rock mass in the goaf; j represents the boundary; K p·j is the expansion coefficient of the caving coal rock mass at the corresponding boundary j; K p·max is the initial expansion coefficient; K p·min is the compaction expansion coefficient; a0 and a1 are the attenuation rates of the caving coal and rock mass relative to the distance from the solid wall and the working face, respectively; d0 and d1 are the distances from point (x, y) to the solid wall and the working surface, respectively; ξ1 is the adjustment number for controlling the distribution shape of the "O" ring model; S3, the height H of the caving goaf and the porosity n are expressed as functions of the expansion coefficient: Where: H is the caving height of the goaf; n is the porosity of the goaf; M is the mining height of the working face; The relationship between the permeability of the porous medium in the goaf and the porosity n of the goaf is expressed by the Blake-Kozeny equation: Where: d p is the particle diameter of the porous medium in the goaf; S4. Gas flow control equations Considering that the highly dynamic change of coal and rock mass in the goaf under continuous advancement of the working face is an important constraint on the flow field in the goaf, the mass conservation equation of gas flow in the goaf under two-dimensional steady state is obtained: Where: v g is the velocity vector of the mixed gas in the goaf; Q s is the source term of the gas; Darcy's law is used to describe the flow of gas in porous media in the goaf: Where: p is the mixed gas pressure in the goaf; μ is the dynamic viscosity coefficient of the mixed gas in the goaf; ρ g is the mixed gas density in the goaf; Substituting formula (6) into formula (5), the control equation of gas flow in the goaf is obtained: S5. Gas Convection Diffusion Equation The gas flow in the goaf satisfies the convection-diffusion equation. Substituting the gas velocity calculated from the gas flow control equation into the convection-diffusion equation, the gas concentration distribution law in the goaf is obtained as follows: Where: is the gas concentration; is the gas sink in the goaf; c is the concentration of the mixed gas components, c = p / RT g ; R is the gas constant; T g is the gas temperature in the goaf; t is time; is the diffusion coefficient tensor of gas, expressed as: Where: ij is the Kronecker symbol; v i is the component of the gas flow velocity along the x, y, and z axes, and the component in the x and y directions; α L and α T are the longitudinal and transverse diffusion of the gas, respectively; τ is the tortuosity of the porous medium; D a is the molecular diffusion coefficient of gas; Gas emission per unit volume and time Expressed as: Where: is the cumulative gas release intensity per unit area of ​​the goaf; S6. According to the characteristics of gas source release in goaf, gas outburst in goaf mainly comes from gas desorption of floating coal in goaf, gas released from upper and lower adjacent unloaded coal and rock layers affected by mining, and gas outburst from old goaf along a certain local channel. Therefore, the cumulative gas release intensity per unit area of ​​goaf at any point in goaf under continuous advancement of working face is: Expressed as: Where: x0 is the initial position coordinate of the working surface; u is the working face advancement speed; t is the mining time; w0 is the uniform and stable gas source emission intensity in the goaf; w1 is the initial outburst intensity of the gas source of the coal seam and the gas source of the upper unloaded coal and rock layer; λ is the gas release attenuation coefficient; S7. Geometric model and boundary conditions of goaf Based on the collected working face conditions, working face ventilation parameters, and goaf gas emission parameters, a geometric model of the goaf was established. The flow field calculation parameters and boundary conditions are shown in Tables 1 and 2, respectively. In Table 1, p0 is the corner pressure of the working face, L is the length of the working face, R and R1 are the ventilation resistance of the working face and the remaining lane, respectively, Q is the main air volume, and Q1 is the air volume in the remaining lane.

2. The method for calculating gas concentration distribution in goaf under Y-type ventilation of goaf-side entry retaining working face according to claim 1 is characterized in that: The model initial and boundary conditions in Table 1 in step S7 are: 。 3. The method for calculating gas concentration distribution in goaf under Y-type ventilation of goaf-side entry retaining working face according to claim 1 is characterized in that: The numerical simulation parameters in Table 2 in step S7 are: 。

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