WO2021109922A1

WO2021109922A1 - Method for designing width of isolation coal pillar and gasifier in underground gasification under aquifer facing overlying strata

Info

Publication number: WO2021109922A1
Application number: PCT/CN2020/132020
Authority: WO
Inventors: 李怀展; 郭广礼; 查剑锋; 徐友友; 刘潇鹏
Original assignee: 中国矿业大学
Priority date: 2019-12-03
Filing date: 2020-11-27
Publication date: 2021-06-10
Also published as: CA3163363A1; CN110991042B; CN110991042A

Abstract

Disclosed is a method for designing the width of an isolation coal pillar and a gasifier in underground gasification under an aquifer facing an overlying strata, which is suitable for the design of coal mining by underground gasification under the overlying stratum aquifer. The method comprises: firstly, determining the maximum height of a waterproof coal-rock pillar according to the position of an aquifer; calculating the thickness of a protective layer of the area to be gasified, and determining a development limit value of a water-flowing fracture zone of the gasified area; establishing a strip mining-surface mining retreating-type gas injection control underground gasification numerical model, and determining the relationship between the development height of a strip mining-surface mining retreating-type gas injection control underground gasification water-flowing fracture zone and the width of the gasifier and the isolation coal pillar; and selecting, in combination with the relationship between the development height of the water-flowing fracture zone and the width of the gasifier and the isolation coal pillar, the width of the gasifier and the isolation coal pillar for the strip mining-surface mining retreating-type gas injection control underground gasification, thereby completing the safe production design for the strip mining-surface mining retreating-type gas injection control underground gasification under the overlying stratum aquifer. The method is simple in terms of steps, and can ensure the optimal gasification production benefit on the premise of ensuring the stability of the overlying aquifer and the safe production of underground gasification.

Description

Design method for separating coal pillar and gasification furnace width in underground gasification under overlying strata aquifer

Technical field

The invention designs a method for designing the width of the isolated coal pillar and the gasifier in underground gasification, and is particularly suitable for the isolation and gasification of the coal pillar and gasification in underground gasification facing the overburden aquifer used in safe gasification coal mining under the aquifer. Furnace width design method.

technical background

The development of underground coal gasification is not only the need of environmental protection but also one of the important technical directions for the future development of the coal industry, and it is of great significance for improving my country's energy security. The essence of underground coal gasification is not to extract coal, but to extract the energy contained in coal. In 1868, the German scientist Sir William first proposed the idea of underground gasification of coal in situ based on this concept. Since then, the Soviet Union, the United States, Australia and other countries have conducted research on underground coal gasification technology. However, the gasification process at this stage has disadvantages such as many gasification drilling holes, high gasification furnace cost, and high geological and hydrological requirements. Until 1976, the Lawrence Livermore National Laboratory in the United States proposed a controlled injection point retrogressive gasification process (CRIP), which is a well-type underground gasification process, which greatly promotes the underground coal The development of gasification. The research on underground coal gasification in my country started late. It was not until the end of the 1980s that experiments on underground coal gasification began; and the use of abandoned coal lanes in existing coal mines has developed a "long passage, large cross-section, and two-stage" project. Well-type underground gasification process. Since then, my country’s underground coal gasification has developed rapidly. Especially from 2011 to 2014, ENN Gasification Coal Mining Technology Co., Ltd. and China University of Mining and Technology undertook the completion of the National High-Tech Research and Development Program (863 Program) project “Underground Coal Gasification”. "Key technologies for industrialization" research and industrial tests, and proposed a strip mining-face mining retreat type controlled gas injection underground gasification process, which enabled my country to make important progress in the underground coal gasification process without wells.

In order to ensure the success of the underground gasification industrial experiment, the scale of the experimental area is relatively small, and the isolated coal pillars between the gasification surfaces are relatively large. The stability of the gasification furnace and the surrounding rock in the combustion zone is better guaranteed in the experiment. Lead to obvious rock fracture and its hydraulic connection with the aquifer. However, with the promotion and application and the expansion of gasification scale, the overburden cracks in the combustion zone lead to groundwater intrusion into the gasifier will become the core bottleneck restricting the promotion and application of this technology. Especially with the expansion of the combustion zone, the overhanging area of the top plate of the gasification channel continues to increase, which may break under the action of the high temperature thermal stress of the gasifier and the gravity of the overlying rock. When the cracks develop to the aquifer, it will cause groundwater pollution and groundwater intrusion into the gasifier, reducing the gasification efficiency and even causing the gasifier to be scrapped; when the cracks develop to the surface, it will also cause gasification and poisonous gas to gush out and pollute Atmospheric environment in mining area. Therefore, how to rationally design the strip mining-face mining retreat to control the width of the gasifier and the isolated coal pillar in underground gasification, control the development of water-conducting fissures and protect the overlying aquifer is one of the bottlenecks in the promotion and application of this technology.

Many scholars have carried out a lot of research work on the calculation model of overburden crack development height in conventional mine mining, and have established corresponding calculation models for different situations, and have formed a relatively mature theory and method for prediction of overburden crack development height in coal mining. As early as the 1980s, in order to meet the needs of coal mining under water bodies, Chinese scholars summarized and established an empirical formula for the development height of water-conducting fracture zones based on a large amount of measured data, and it has been used after several revisions. This is also the current practical application. The most extensive forecasting method. In recent years, many scholars have established corresponding calculation models for the development height of cracks in overlying strata based on specific issues. For example, Xu Jialin found that the location of the main key layer of the overburden is a key factor affecting the development of the water-conducting fractured zone. On this basis, a method for predicting the height of the water-conducting fractured zone based on the location of the key layer was proposed. Zhang Jixiong used the UDEC numerical simulation software to simulate and analyze the height of the water-conducting fracture zone under the conditions of different mining heights and different filling rates, and established the formula for predicting the height of the water-conducting fracture zone in the filling mining. Expected results. Huang Bingxiang believes that the fracture degree of the thick rock layer is the key to determine whether the rock layer conducts water and gas, and puts forward the concept of rock penetration, and mechanically analyzes the penetration of the overburden fractures. Based on this, a water-transmitting fracture is proposed. Calculation method of belt development height. Zhao Bingchao combined the definition of the generalized damage factor of the middle layer of the rock layer and the water-conducting fracture zone, and derived the relationship between the mining thickness, the thickness of the bedrock, the thickness of the load layer and the generalized damage factor of the water-conducting fracture zone, and simplified the height of the water-conducting fracture zone. Calculation method. Yang Guoyong puts forward a calculation method for the development height of water-conducting fissures based on the analytic hierarchy process-fuzzy cluster analysis method based on mass production practice. The above research results provide an important reference for the establishment of the calculation method for the development of cracks in the overburden rock in the combustion zone of underground gasification controlled gas injection in strip mining and face mining. However, at present, there is no relevant research on how to design the width of the gasifier and the isolated coal pillar in the underground gasification controlled injection underground gasification. Therefore, there is currently a lack of a design method for the separation of coal pillars and the width of the gasifier in underground gasification controlled gas injection under the strip mining-face mining under the overlying water layer.

Summary of the invention

In response to the above problems, a simple step is provided that can effectively solve the problem of isolating coal pillars and gasifiers in underground gasification and how to protect the overlying aquifers. The problem of isolating coal pillars and gasifiers in underground gasification facing overlying aquifers is provided. Design method of gasifier width.

In order to achieve the above technical objectives, the method for designing the width of the isolated coal pillar and the gasifier in underground gasification facing the overburden aquifer of the present invention includes the following steps:

a Determine the maximum height of the waterproof coal rock pillar based on the hydrogeological data and the position of the aquifer in the gasification area;

b Use the calculated thickness of the protective layer to determine the limit for the development of the gasification coal mining water-conducting fracture zone in the study area;

c Use the collected geological data of the gasification area and the mechanical parameters of each rock layer to establish a numerical model of strip mining-face mining retreat controlled gas injection underground gasification based on the numerical simulation method. In the numerical model, the design isolation coal pillar width is 4m～35m, gas The width of the furnace is 4m～35m. Combine all the width of the gasifier and the width of the isolated coal pillar to form a set of data and arrange all the combined data. Use the numerical model to calculate the lower water-conducting fissure zone of the data set of different isolated coal pillars and gasifier widths Correspondingly match the development height data of all water-conducting fissure zones with the width of the gasifier and the width of the isolated coal pillar, so as to obtain and then obtain the development of strip mining-face mining retreat control gas injection underground gasification and water-conducting fissure zone development The relationship between the height and the width of the gasifier and the width of the isolated coal pillar data set;

d Finally, according to the known development limits of the water-conducting fractured zone in the study area, combined with strip mining-face mining retreat to control the relationship between the development height of the gas-injected underground gasification water-conducting fracture zone, the width of the isolated coal pillar, and the width of the gasifier. , Combined with the established limits for the development of water-conducting fissure zones, and based on the relationship between the height of the development of the water-conducting fissured zones, the width of the isolated coal pillars and the width of the gasifier, select the water-conducting fissured zones that are closest to the limit and smaller than the limit The combination of isolated coal pillars and gasifier width data with matching height values is the optimal gasification zone strip mining-face mining retreat type to control the isolated coal pillars and gasifier width for underground gasification by gas injection, and complete the design.

The specific steps are:

Step 1: For the coal mining area under the overburden aquifer gasification, collect the hydrogeological data, drilling diagrams and other data of the coal mining area to be gasified, and clarify the location of the aquifer and water barrier of the overburden rock in the gasification area. Further according to the position of the aquifer to determine the maximum water height H of the pillar coal _anti ensure the maximum height H from the _anti waterproof coal seam is less than the pillar to the aqueous layer; the waterproof coal pillar mining means to ensure the safety of water body The designed maximum coal seam mining limit is the coal and rock mass at the bottom of the water body;

Step 2: According to the calculation formula of the protective layer thickness of the waterproof coal and rock pillars in the "Buildings, water bodies, railways, and main shafts and coal pillars and coal mining specifications", combined with the geological mining conditions and overburden in the area to be gasified lithology, calculating the protective layer thickness H and thus _protect the gasification zone of the gasification zone to obtain the proposed water flowing fractured zone limit _{limit conduction} H = H -H _anti _protection;

Step 3: According to the geological mining conditions, working face distribution, in-situ stress monitoring results, and rock mechanics parameter change data at different temperatures in the pseudo-gasification area, use ANSYS software to establish strip mining-face mining retrograde control gas injection underground gasification values The model is divided into grids, and the established strip mining-face mining retreat controlled gas injection underground gasification numerical model is imported into FLAC3D to calculate the development height of the water-conducting fissure zone. Due to the high temperature effect of the surrounding rock in the combustion zone of underground coal gasification, Therefore, mechanical experiments are carried out on the rock layers within 15m of the coal seam floor, 10m width of the coal seam and 20m of the roof in the study area to obtain the compressive strength, tensile strength, and cohesion between 30° and 1000° with temperature of the floor, raw coal and roof in the pseudo gasification area The relationship between compressive strength, tensile strength, cohesion and temperature is displayed by mathematical expressions, and the relationship between compressive strength, tensile strength, cohesion and temperature is embedded in FLAC3D in combination with the distribution law around the temperature field. The model calculates the height of the water-conducting fracture zone, and finally uses the stress analysis method to determine the height of the underground gasification water-conducting fracture zone;

The width of the designed isolated coal pillar is 4m～35m, and the width of the gasifier is 4m～35m. According to the simulation plan, the established numerical model is used to calculate the width of different gasifiers and isolated coal pillars. H ₁ , H ₂ , H ₃ , ... H _n , so as to determine the development height of the water-conducting fissure zone and the width of the gasification furnace and the isolated coal pillar. relationship;

Step 4: The proposed gasification zone Fractured guide height limit H and different _{limit pilot} air conduction water fractured zone height H _{_{_{1, H 2, H 3,}}} ... H n one by one, selects satisfying H _i ≤H _{lead limit} and the data closest to the index H _{lead limit} _{, H i} is the best value, and at the same time, according to the best value H _i , the gasifier and segregated coal for strip mining-face mining retreat type controlled gas injection underground gasification are selected The width of the column, and then complete the design of the width of the coal column and the gasifier in the underground gasification of the overburden aquifer under the strip mining-face mining retreat type controlled gas injection underground gasification.

The thickness of the protective layer in the waterproof and safe coal pillars under the conditions of gently inclined and inclined coal seams is selected according to the values in the following table:

In the table, A is the thickness of the coal seam.

Beneficial effects:

The present invention considers the high temperature effect of the surrounding rock in the gas injection underground gasification combustion zone in consideration of strip mining-face mining, and takes into account the development control of the water-conducting fracture zone and the protection of the overburden aquifer, and creatively proposes the continuous mining under the overburden aquifer. -The design method for the production design of back-face controlled gas injection underground gasification, which solves the design of the width of the gasifier and the isolated coal pillar in the popularization and application of the back-face controlled gas injection underground gasification and how to control the development of water-conducting fissures, The difficult problem of protecting overburden aquifers has simple steps and small calculations. It has important practical significance and application value for the design of gasification coal mining under the overburden aquifers, the development control of water conducting fissures, and the protection of overburden aquifers.

Description of the drawings

Fig. 1 is a design flow chart of the width of the isolated coal pillar and the gasifier in the underground gasification under the overburden aquifer implemented in the present invention.

Figure 2(a) shows the relationship between the compressive strength and high temperature of the rock formation in the Ulanchabu mine strip mining-face mining receding controlled gas injection underground gasification field.

Figure 2(b) shows the relationship between the elastic modulus of the rock formation and the high temperature of the Ulanchabu mine strip mining-face mining retreat controlled gas injection underground gasification field.

Figure 3 shows the distribution law of the temperature field in the cross section of the combustion zone of the underground gasification field controlled by gas injection from strip mining to face mining in the Ulan Chabu Mine.

Detailed ways

The following will further describe the present invention in detail with reference to the drawings and the specific implementation process:

As shown in Figure 1, the design method of separating coal pillar and gasification furnace width in underground gasification facing the overburden aquifer, the steps are as follows:

c Use the collected geological data of the gasification area and the mechanical parameters of each rock layer to establish a numerical model of underground gasification controlled by the strip mining-face mining retreat type controlled gas injection based on the numerical simulation method. In the numerical model, the design isolation coal pillar width is 4m～35m, gas The width of the furnace is 4m～35m. Combine all the widths of the gasifier and the width of the isolated coal pillar to form a set of data and arrange all the combined data. Use the numerical model to calculate the lower water-conducting fracture zone of the data set for different isolated coal pillars and the width of the gasifier Correspondingly match the development height data of all water-conducting fissure zones with the width of the gasifier and the width of the isolated coal pillar, so as to obtain and then obtain the development of strip mining-face mining retreat control gas injection underground gasification and water-conducting fissure zone development The relationship between the height and the width of the gasifier and the width of the isolated coal pillar; different gasifier widths and the width of the isolated coal pillar correspond to the height of a water-conducting fissure zone. For example, the gasifier has a width of 4m and an isolated coal pillar width of 5m, and there will be a water-conducting fissure zone height h ₁ ; a gasifier width of 4m and an isolated coal pillar width of 5m will also have a water-conducting fissure zone height h ₂ ; With a width of 5m and a water-conducting fissure zone width of 5m, there will also be a water-conducting fissure zone height h ₃ .

Example one,

A design method for separating coal pillar and gasifier width in underground gasification under overburden aquifer, the steps are:

c At the same time, based on the numerical simulation method, use the collected geological data of the gasification area and the mechanical parameters of each rock layer to establish a numerical model of strip mining-face mining with retreat controlled gas injection underground gasification, and the design isolation coal pillar width is 4m～35m, the numerical model Input in sequence: 4m, 5m, 6m, 7m, 8m, 9m, 10m, 11m, 12m, 13m, 14m, 15m, 16m, 17m, 18m, 19m, 20m, 21m, 22m, 23m, 24m, 25m, 26m, 27m , 28m, 29m, 30m, 31m, 32m, 33m, 34m, 35m, and the gasifier width is 4m～35m: 4m, 5m, 6m, 7m, 8m, 9m, 10m, 11m, 12m, 13m, 14m, 15m , 16m, 17m, 18m, 19m, 20m, 21m, 22m, 23m, 24m, 25m, 26m, 27m, 28m, 29m, 30m, 31m, 32m, 33m, 34m, 35m design plan, using the established strip mining- The numerical model of underground gasification controlled by face mining with receding gas injection calculates the height of the water-conducting fissure zone under different isolation coal pillars and gasifier widths, and then determines the development of water-conducting fissure zone in strip mining-face mining receding controlled gas injection underground gasification The relationship between the height and the width of the gasifier and the isolated coal pillar;

d Finally, according to the development limit of the water-conducting fracture zone determined in the study area, combined with the strip mining-face mining retreat type to control the development height of the gas-injected underground gasification water-conducting fracture zone and the relationship between the isolated coal pillar and the width of the gasifier, the gas is selected The width of the isolated coal pillar and gasifier for underground gasification controlled by the strip mining-face mining with retrograde control of the gasification area, and then the isolated coal pillars in the overlying aquifer under the strip mining-face mining with retrograde gas injection controlled and controlled gasification underground gasification Design with the width of the gasifier.

The specific steps are:

Step 1: For the coal mining area under the overburden aquifer gasification, collect the hydrogeological data, drilling diagrams and other data of the coal mining area to be gasified, and clarify the location of the aquifer and water barrier of the overburden rock in the gasification area. Further waterproof coal pillar determines the maximum height H according to a position _preventing the aquifer; water mining coal seam upper pillar refers to mining safety ensuring water to the bottom of the body of water is designed coal, rock.

Step 2: According to the calculation formula of the protective layer thickness of the waterproof coal and rock pillars in the "Buildings, water bodies, railways, and main shafts and coal pillars and coal mining specifications", combined with the geological mining conditions and overburden in the area to be gasified lithology, thickness of the protective layer is calculated _Paul H gasification zone, thereby to obtain limit _guide water flowing fractured zone H Quasi gasification zone _limit = H -H _prevention _protection. The thickness of the protective layer in the waterproof and safe coal pillar can be selected according to the values in Table 1 under the conditions of gently inclined and inclined coal seams.

Table 1 The thickness of the protective layer of the waterproof and safe coal and rock pillars under the mining conditions of gently inclined and inclined coal seams

The thickness of the protective layer is calculated according to the above table. The calculation of the thickness of the protective layer is the nature of the overburden and the burial conditions, and then the thickness of the protective layer is determined to be 3A or 4A or 5A, where A is the thickness of the coal seam. For example, if there is no clay layer at the bottom of the loose layer, the thickness of the protective layer is 6A. If the coal thickness is 3 meters, the thickness of the protective layer is 18 meters;

Step 3: According to the geological mining conditions, working face distribution, in-situ stress monitoring results, and rock mechanics parameter change data at different temperatures in the pseudo-gasification area, use ANSYS software to establish strip mining-face mining retrograde control gas injection underground gasification values The model is divided into grids, and the established strip mining-face mining retreat controlled gas injection underground gasification numerical model is imported into FLAC3D for calculation to obtain the development height of the water-conducting fractured zone. Taking into account the high temperature effect of the surrounding rock in the combustion zone of underground coal gasification, high temperature tests were carried out on the compressive strength and elastic modulus of the bottom and roof of the coal seam in the underground gasification area, and the compression resistance of the bottom and roof of the gasification area was obtained. The change law of strength and elastic modulus with temperature is shown in Figure 2. Combined with strip mining-face mining retreat type control gas injection underground gasification test field combustion zone surrounding rock temperature field distribution law, as shown in Figure 3, using the fish language to embed the relationship between compressive strength, elastic modulus and temperature into The FLAC3D model calculates the height of the water-conducting fracture zone, and uses the stress analysis method to determine the height of the underground gasification water-conducting fracture zone.

The design isolation coal pillar width is 4m～35m: 4m, 5m, 6m, 7m, 8m, 9m, 10m, 11m, 12m, 13m, 14m, 15m, 16m, 17m, 18m, 19m, 20m, 21m, 22m, 23m, 24m, 25m, 26m, 27m, 28m, 29m, 30m, 31m, 32m, 33m, 34m, 35m, and the gasifier width is 4m～35m: 4m, 5m, 6m, 7m, 8m, 9m, 10m, 11m, Design schemes of 12m, 13m, 14m, 15m, 16m, 17m, 18m, 19m, 20m, 21m, 22m, 23m, 24m, 25m, 26m, 27m, 28m, 29m, 30m, 31m, 32m, 33m, 34m, 35m According to the simulation plan, the established numerical model is used to calculate the height of the water-conducting fissure zone H ₁ , H ₂ , H ₃ ,… H of the strip mining-face mining receding controlled gas injection underground gasification under different gasification furnaces and isolated coal pillar widths. _n . In this way, the relationship between the development height of the water-conducting fissure zone and the width of the gasification furnace and the isolated coal pillar can be determined for the strip mining-face mining retreat type controlled gas injection underground gasification.

_{Step 4: The limit H lead limit of the} development height of the water-conducting fissure zone in the pseudo-gasification area obtained in step 2 and the different gasification furnace and isolated coal pillar width obtained in step 3 under strip mining-face mining retreat controlled injection _{The development heights H 1} , H ₂ , H ₃ , ... H _n of the water-conducting fissure zone of underground gasification are compared one by one, _{and the data that meets H i} ≤ _{H lead limit} and is closest to the index H _{lead limit} is selected, and at the same time, according to the best The value H _i selects the gasifier and the width of the isolation coal pillar for the strip mining-face mining retrograde controlled gas injection underground gasification, and then completes the isolation in the strip mining-face mining retrograde controlled gas injection underground gasification under the overburden aquifer Design of coal pillar and gasifier width.

Claims

A design method for separating coal pillars and gasification furnace width in underground gasification under overlying aquifers, which is characterized by:

a Determine the maximum height of the waterproof coal rock pillar based on the hydrogeological data and the position of the aquifer in the gasification area;

b Use the calculated thickness of the protective layer to determine the limit for the development of the gasification coal mining water-conducting fracture zone in the study area;

c Use the collected geological data of the gasification area and the mechanical parameters of each rock layer to establish a numerical model of strip mining-face mining retreat controlled gas injection underground gasification based on the numerical simulation method. In the numerical model, the design isolation coal pillar width is 4m～35m, gas The width of the furnace is 4m～35m. Combine all the width of the gasifier and the width of the isolated coal pillar to form a set of data and arrange all the combined data. Use the numerical model to calculate the lower water-conducting fissure zone of the data set of different isolated coal pillars and gasifier widths Correspondingly match the development height data of all water-conducting fissure zones with the width of the gasifier and the width of the isolated coal pillar, so as to obtain and then obtain the development of strip mining-face mining retreat control gas injection underground gasification and water-conducting fissure zone development The relationship between the height and the width of the gasifier and the width of the isolated coal pillar data set;

d Finally, according to the known development limits of the water-conducting fractured zone in the study area, combined with strip mining-face mining retreat to control the relationship between the development height of the gas-injected underground gasification water-conducting fracture zone, the width of the isolated coal pillar, and the width of the gasifier. , Combined with the established limits for the development of water-conducting fissure zones, and based on the relationship between the height of the development of the water-conducting fissured zones, the width of the isolated coal pillars and the width of the gasifier, select the water-conducting fissured zones that are closest to the limit and smaller than the limit The combination of isolated coal pillars and gasifier width data with matching height values is the optimal gasification zone strip mining-face mining retreat type to control the isolated coal pillars and gasifier width for underground gasification by gas injection, and complete the design.
The production design method for underground gasification under the overburden aquifer according to claim 1, characterized in that the specific steps are:

Step 1: For the coal mining area under the overburden aquifer gasification, collect the hydrogeological data, drilling diagrams and other data of the coal mining area to be gasified, and clarify the location of the aquifer and water barrier of the overburden rock in the gasification area. Further according to the position of the aquifer to determine the maximum water height H of the pillar coal anti ensure the maximum height H from the anti waterproof coal seam is less than the pillar to the aqueous layer; the waterproof coal pillar mining means to ensure the safety of water body The designed maximum coal seam mining limit is the coal and rock mass at the bottom of the water body;

Step 2: According to the calculation formula for the thickness of the protective layer reserved for the water-proof coal and rock pillars in the "Code for the Setting of Coal Pillars in Buildings, Water, Railways, and Main Roadways and Compressed Coal Mining", combined with the geological mining conditions and overburden in the area to be gasified lithology, calculating the protective layer thickness H and thus protect the gasification zone of the gasification zone to obtain the proposed water flowing fractured zone limit limit conduction H = H -H anti protection;

Step 3: According to the geological mining conditions, working face distribution, in-situ stress monitoring results, and rock mechanics parameter change data at different temperatures in the pseudo-gasification area, use ANSYS software to establish strip mining-face mining retrograde control gas injection underground gasification values The model is divided into grids, and the established strip mining-face mining retreat controlled gas injection underground gasification numerical model is imported into FLAC3D to calculate the development height of the water-conducting fissure zone. Due to the high temperature effect of the surrounding rock in the combustion zone of underground coal gasification, Therefore, mechanical experiments were carried out on the rock layers within 15m of the coal seam floor, 10m width of the coal seam and 20m of the roof in the study area to obtain the compressive strength, tensile strength, cohesive force of the floor, raw coal and roof in the pseudo-gasification area with temperature. The relationship between compressive strength, tensile strength, cohesion and temperature is displayed by mathematical expressions, and the relationship between compressive strength, tensile strength, cohesion and temperature is embedded in FLAC3D in combination with the distribution law around the temperature field. The model calculates the height of the water-conducting fracture zone, and finally uses the stress analysis method to determine the height of the underground gasification water-conducting fracture zone;

The width of the designed isolated coal pillar is 4m～35m, and the width of the gasifier is 4m～35m. According to the simulation plan, the established numerical model is used to calculate the width of different gasifiers and isolated coal pillars. H 1 , H 2 , H 3 , ... H n , so as to determine the development height of the water-conducting fissure zone and the width of the gasification furnace and the isolated coal pillar. relationship;

Step 4: The proposed gasification zone Fractured guide height limit H and different limit pilot air conduction water fractured zone height H 1, H 2, H 3, ... H n one by one, selects satisfying H i ≤H lead limit and the data closest to the index H lead limit , H i is the best value. At the same time, according to the best value H i , the gasifier and segregated coal for strip mining-face mining retreat type controlled gas injection underground gasification are selected The width of the column, and then complete the design of the width of the coal column and the gasifier in the underground gasification of the overburden aquifer under the strip mining-face mining retreat type controlled gas injection underground gasification.
The method for designing the width of the isolated coal pillar and the gasifier in underground gasification facing the overburden aquifer according to claim 1, wherein the protection layer in the coal pillar is waterproof and safe under the conditions of gently inclined and inclined coal seam mining The thickness is selected according to the values in the table below:

In the table, A is the thickness of the coal seam.