Method for designing width of isolation coal pillar and gasifier in underground gasification under aquifer facing overlying strata
Patent Information
- Application Number
- CA3163363
- Authority / Receiving Office
- CA · CA
- Patent Type
- Patents
- Current Assignee / Owner
- Priority Date
- 2019-12-03
- Filing Date
- 2020-11-27
- Publication Date
- 2026-09-15
- Estimated Expiration
- 2040-11-27
Abstract
Description
Description METHOD FOR DESIGNING WIDTH OF ISOLATION COAL PILLAR AND GASIFIER IN UNDERGROUND GASIFICATION UNDER AQUIFER FACING OVERLYING STRATA Technical Field The present invention relates to a design method for a width of an isolated coal pillar and a width of a gasification furnace in underground gasification, in particular to a design method for the width of the isolated coal pillar and the width of the gasification furnace in underground gasification under an overburden aquifer, which is applicable to in safe coal gasification mining under an aquifer. Background Art Developing underground coal gasification is not only a need for 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 the energy security in China. In essence, underground coal gasification is not to mine out the coal but to extract the energy contained in the coal. In 1868, based on that concept, a German scientist Sir William first proposed an ideal of treating coal by in-situ underground gasification. After that, researches on the underground coal gasification process were carried out in many countries, including USSR, USA, and Australia, etc. However, the gasification process at that phase had disadvantages such as a large number of gasification boreholes, high cost for underground gasification, and high hydrogeological requirements, etc. Until 1976, Lawrence Livermore National Laboratory in USA put forward a controlled retreating injection point (CRIP) gasification process, which was a well-free underground gasification process and greatly promoted the development of underground coal gasification. In China, the research on underground coal gasification started late, and underground coal gasification experiments were not carried out until the end of 1980s; a long-tunnel large-section two-stage well-type underground gasification process was developed by utilizing the abandoned coal roadways in the existing coal mines. After that, underground coal gasification was developed rapidly in China. Especially, from year 2011 to year 2014, Xinao Coal Gasification and Mining Technology Co., Ltd. and China University of Mining and Technology undertook and accomplished the research and industrial test for the project "Key Techniques for Industrialization of Underground Coal Gasification" in the National High-Tech Research and Development Program (Program 863), and put forward a retreating controlled gas injection and underground gasification process for strip-face mining, which represented an important progress in the well-free underground coal gasification process in China. To ensure the success of the industrial experiment on underground gasification, the test area was relatively small, and the isolated coal pillars between the gasification faces were relatively large. In the test, the stability of the gasification furnace and the surrounding rock of the burnt-out zone were maintained well, without any obvious rock stratum fracture and relevant hydraulic connection with the aquifer. However, as the process is applied widely and the gasification is scaled up, the ingress of groundwater into the gasification furnace incurred by the fissures in the overlying strata of the burnt- out zone has become an essential bottleneck problem hindering the wide application of the process. Especially, as the burnt-out zone is expanded, the exposed area of the roof of the gasification tunnels was increased continuously, and the roof may be fractured under the high temperature and thermal stress of the gasification furnace and the gravity action of the overlying rock. When the fissures develop to the aquifer, the ground water mass will be contaminated and the ground water will invade the gasification furnace, consequently the gasification efficiency will be degraded and even the gasification furnace has to be discarded; when the fissures develop to the ground surface, the toxic gas from the gasification may gush out and pollute the atmospheric environment of the mining area. It is one of the bottleneck problems to reasonably design the width of the gasification furnace and the width of the isolated coal pillars in retreating controlled gas injection and underground gasification for strip-face mining to control the development of the water flowing fracture zone and protect the overburden aquifer in the wide application of the process. Many researchers have carried out a lot of research work on calculation models of the development height of the fissures in the overlying strata during coal mining under conventional well conditions, and have established corresponding calculation models for different situations, thereby have established a matured theory and method for predicting the development height of the fissures in the overlying strata during coal mining. Early in the 1980s, in order to meet the demand for coal mining under water bodies, Chinese researchers summarized and established empirical formulae for predicting the development height of the water flowing fractured zone on the basis of massive field survey and measurement data, and the empirical formulae were revised in several rounds and have been used up to now, and are also the most widely used prediction method at present. In recent years, many researchers have established corresponding calculation models of the development height of fissures in the overlying strata for specific situations. For example, XU, Jialin found that the position of the main key stratum of the overlying strata was a key factor affecting the development of the water flowing fractured zone, and, on that basis, proposed a method for predicting the height of the water flowing fractured zone based on the position of the key stratum. ZHANG, Jixiong utilized UDEC numerical simulation software to simulate and analyze the height of the water flowing fractured zone under different mining height and different filling ratio conditions, established a prediction formula for predicting the height of the water flowing fractured zone in backfill mining, and compared the prediction result with the field measurement result finally, indicating that a better prediction result was achieved. HUANG, Bingxiang believed that the fracture degree of a thick rock stratum was a key determinant for water conduction and gas permeation through the rock stratum, and put forward a concept of rock penetration degree, carried out mechanical analysis on the penetration degree of fractures and fissures through the overlying strata, and, on that basis, proposed a method for calculating the development height of the water flowing fractured zone. ZHAO, Bingchao derived a relationship between mining thickness, bedrock thickness, bearing layer thickness and a generalized damage factor of water flowing fractured zone on the basis of the definitions of intermediate rock strata and generalized damage factor of water flowing fractured zone, and simplified the calculation method of the height of water flowing fractured zone. Through a large quantity of production practices, YANG, Guoyong proposed a calculation method for calculating the development height of water flowing fractures based on analytic hierarchy process-fuzzy clustering analysis. The above research results provide an important reference for working out a calculation method for calculating the development height of the fissures in the overlying strata of the burnt-out zone in retreating controlled gas injection and underground gasification for strip-face mining. However, at present, there is no related research on the design of the width of the gasification furnace and the width of the isolated coal pillars in retreating controlled gas injection and underground gasification for strip-face mining under an overburden aquifer. Therefore, at present, there is no method for designing the width of the isolated coal pillars and the width of the gasification furnace in retreating controlled gas injection and underground gasification for strip-face mining under an overburden aquifer. Contents of the Invention In view of the above problems, the present invention provides a design method for the width of an isolated coal pillar and the width of the gasification furnace in underground gasification under an overburden aquifer, which has simple steps and practically solves the problems in the design of isolated coal pillars and gasification furnace in underground gasification and protection of the overlying aquifer. To attain the technical object described above, the design method for the width of the isolated coal pillar and the width of the gasification furnace in underground gasification under an overburden aquifer provided by the present invention comprises the following steps: a. determining the maximum height of waterproof coal rock pillars according to the hydrological data and the position of the aquifer in the area to be gasified; b. determining a limit for the development of water flowing fractured zones in the study area to be gasified for coal mining by using the obtained thickness of a protective seam through calculation; C. establishing a numerical model of retreating controlled gas injection and underground gasification for strip-face mining with a numerical simulation method by using collected hydrogeological data and mechanical parameters of the rock strata in the gasification area, setting the design width of the isolated coal pillars to 4m to 35m and setting the design width of the gasification furnace to 4m to 35m in the numerical model, combining the width of the gasification furnace and the width of the isolated coal pillars to form a data set and arranging all combined data, calculating the development height of the water flowing fractured zones against different data sets of the width of the isolated coal pillars and the width of the gasification furnace, mapping all the data of the development height of the water flowing fractured zones to the data sets of the width of the gasification furnace and the width of the isolated coal pillars, thereby obtaining a relationship between the development height of the water flowing fractured zones and the data sets of the width of the gasification furnace and the width of the isolated coal pillars in retreating controlled gas injection and underground gasification for strip-face mining; d. selecting a data combination of the width of the isolated coal pillars and the width of the gasification furnace corresponding to a value of the development height of the water flowing fractured zones, which is the closest to but smaller than the limit for the development of the water flowing fractured zones, according to the known limit for the development of the water flowing fractured zones in the study area, in conjunction with the relationship between the development height of the water flowing fractured zones and the data sets of the width of the isolated coal pillars and the width of the gasification furnace in retreating controlled gas injection and underground gasification for strip-face mining, the determined limit for the development of the water flowing fractured zones, and the obtained relationship between the development height of the water flowing fractured zones and the width of the isolated coal pillars and the width of the gasification furnace, and taking the data combination as optimal width of the isolated coal pillars and optimal width of the gasification furnace in retreating controlled gas injection and underground gasification for strip-face mining in the gasification area, thereby finishing the design. The specific steps are as follows: step 1: collecting the data of the coal mining area to be gasified, including the hydrogeological data and the drilling location map in the area to be gasified for coal mining under overburden aquifer, ascertaining the positions of the overburden aquifer and the confining bed in the area to be gasified, and determining the maximum height <com:Math><semantics>Hwaterproof<annotation encoding="application / x-tex">H_{waterproof}< / annotation>< / semantics>< / com:Math> of the waterproof coal rock pillars according to the position of the aquifer, to ensure that the maximum height <com:Math><semantics>Hwaterproof<annotation encoding="application / x-tex">H_{waterproof}< / annotation>< / semantics>< / com:Math> of the waterproof coal rock pillars is smaller than the distance from the coal seam to the aquifer; wherein the waterproof coal rock pillars refer to the coal and rock mass from the upper limit of coal seam mining to the bottom of the water body designed to ensure safe coal mining under the water body; step 2: calculating the thickness <com:Math><semantics>Hprotection<annotation encoding="application / x-tex">H_{protection}< / annotation>< / semantics>< / com:Math> of the protective seam in the area to be gasified with the calculation formula of the thickness of the protective seam reserved for waterproof coal rock pillars as specified in "Specification for Coal Pillar Reservation and Coal Mining under Buildings, Water Bodies, Railroads and Main Roadways" with reference to the geological mining conditions and the lithology of the overlying strata in the area to be gasified, thereby obtaining a limit <com:Math><semantics>Hflowlimit<annotation encoding="application / x-tex">H_{flow\ limit}< / annotation>< / semantics>< / com:Math> for the water flowing fractured zones in the area to be gasified, and <com:Math><semantics>Hflow_limit=Hwaterproof−Hprotection<annotation encoding="application / x-tex">H_{flow\_limit} = H_{waterproof} - H_{protection}< / annotation>< / semantics>< / com:Math>; step 3: establishing a numerical model of retreating controlled gas injection and underground gasification for strip-face mining with ANSYS<com:Sup>TM< / com:Sup> software according to the geological mining conditions, the distribution of the working faces, the ground stress monitoring result, and the profile of mechanical parameter change of the rock at different temperatures in the area to be gasified, dividing the grids, importing the established numerical model of retreating controlled gas injection and underground gasification for strip-face mining into FLAC3D<com:Sup>TM< / com:Sup> and calculating the development height of the water flowing fractured zones; in view of a high-temperature effect of the surrounding rock in the burnt-out zone of underground coal gasification, carrying out mechanical experiments on the rock strata within the range of 15m distance from the seam floor, 10m distance from the coal seam in the width direction, and 20m distance from the roof to obtain the compression strength and tensile strength of the seam floor, raw coal and roof, a change law of cohesion change with temperature within the range of 30°C to 1,000°C in the area to be gasified, displaying the relationship between compression strength, tensile strength and cohesion and temperature with mathematical expressions, utilizing Fish language<com:Sup>TM< / com:Sup> to insert the relationship between compression strength, tensile strength and cohesion and temperature according to the distribution of the surrounding temperature field into the FLAC3D<com:Sup>TM< / com:Sup> model and calculating the height of the water flowing fractured zone, and finally determining the development height of the water flowing fractured zone in underground gasification with a stress analysis method; setting the design width of isolated coal pillars to 4m to 35m and setting the design width of gasification furnace to 4m to 35m, calculating the height <com:Math><semantics>H1<annotation encoding="application / x-tex">H_1< / annotation>< / semantics>< / com:Math>, <com:Math><semantics>H2<annotation encoding="application / x-tex">H_2< / annotation>< / semantics>< / com:Math>, <com:Math><semantics>H3<annotation encoding="application / x-tex">H_3< / annotation>< / semantics>< / com:Math>, ..., <com:Math><semantics>Hn<annotation encoding="application / x-tex">H_n< / annotation>< / semantics>< / com:Math> of the water flowing fractured zones in retreating controlled gas injection and underground gasification for strip-face mining against different values of the width of the gasification furnace and the width of the isolated coal pillars with the established numerical model according to the simulation scheme, thereby determining the relationship between the development height of the water flowing fractured zones and the width of the gasification furnace and the width of the isolated coal pillars in retreating controlled gas injection and underground gasification for strip-face mining; step 4: comparing the limit <com:Math><semantics>Hflowlimit<annotation encoding="application / x-tex">H_{flow\ limit}< / annotation>< / semantics>< / com:Math> for the development height of the water flowing fractured zones in the area to be gasified with the obtained values <com:Math><semantics>H1,H2,H3,…,Hn<annotation encoding="application / x-tex">H_1, H_2, H_3, \dots, H_n< / annotation>< / semantics>< / com:Math> of the development height of the water flowing fractured zones and selecting a value that meets a criterion <com:Math><semantics>Hi≤Hflowlimit<annotation encoding="application / x-tex">H_i \leq H_{flow\ limit}< / annotation>< / semantics>< / com:Math> and is the closest to the limit <com:Math><semantics>Hflowlimit<annotation encoding="application / x-tex">H_{flow\ limit}< / annotation>< / semantics>< / com:Math> as an optimal value <com:Math><semantics>Hi<annotation encoding="application / x-tex">H_i< / annotation>< / semantics>< / com:Math>, and selecting the width of the gasification furnace and the width of the isolated coal pillars in retreating controlled gas injection and underground gasification for strip-face mining according to the optimal value <com:Math><semantics>Hi<annotation encoding="application / x-tex">H_i< / annotation>< / semantics>< / com:Math>, thereby finishing the design of the width of the isolated coal pillars and the width of the gasification furnace in retreating controlled gas injection and underground gasification for strip-face mining under overburden aquifer. Under gently inclined coal seam and inclined coal seam mining conditions, the thickness of the protective seam in the waterproof and safety coal rock pillars is selected from the following table: [Image disponible dans le document PDF, Image available in the PDF document] In the table, "A" is the thickness of the coal seam. Beneficial effects: in consideration of the high-temperature effect of the surrounding rock in the burnt-out zone in retreating controlled gas injection and underground gasification for strip-face mining in conjunction with water flowing fractured zone development control and overburden aquifer protection, the present invention proposes an inventive production design method for retreating controlled gas injection and underground gasification for strip-face mining under an overburden aquifer, which solves the problems in the design of the width of the gasification furnace and the width of the isolated coal pillars, water flowing fractured zone development control, and overburden aquifer protection in the application of retreating controlled gas injection and underground gasification for strip-face mining, has simple steps and low computation load, and is of great significance and practical application value for the design of coal gasifying extraction under an overburden aquifer, water flowing fractured zone control, and overburden aquifer protection, etc. Brief Description of Drawings FIG. 1 is a flow chart of the isolated coal pillar and gasification furnace width design for underground gasification under an overburden aquifer in the present invention; FIG. 2(a) shows the relationship between the compression strength of the rock strata and high temperature in retreating controlled gas injection and underground gasification for strip-face mining in the Ulanqab Coal Mine; FIG. 2(b) shows the relationship between the elastic modulus of the rock strata and high temperature in retreating controlled gas injection and underground gasification for strip-face mining in the Ulangab Coal Mine; FIG. 3 shows the temperature field distribution on the cross section of the burnt-out zone in retreating controlled gas injection and underground gasification for strip-face mining in the Ulanqab Coal Mine. Embodiments Hereunder the present invention will be further detailed in specific embodiments, with reference to the accompanying drawings. As shown in FIG. 1, a design method for a width of an isolated coal pillar and a width of a gasification furnace in underground gasification under an overburden aquifer in the present invention comprises the following steps: a. determining the maximum height of waterproof coal rock pillars according to the hydrological data and the position of the aquifer in the area to be gasified; b. calculating the thickness of a protective seam, and determining a limit for the development of water flowing fractured zones in the study area where gasification and coal mining are to be carried out; C. establishing a numerical model of retreating controlled gas injection and underground gasification for strip-face mining with a numerical simulation method by using collected hydrogeological data and mechanical parameters of the rock strata in the area to be gasified, setting the design width of the isolated coal pillars to 4m to 35m and setting the design width of the gasification furnace to 4m to 35m in the numerical model, combining the width of the gasification furnace and the width of the isolated coal pillars to form a data set and arranging all combined data, calculating the development height of the water flowing fractured zones against different data sets of the width of the isolated coal pillars and the width of the gasification furnace, mapping all the data of the development height of the water flowing fractured zones to the data sets of the width of the gasification furnace and the width of the isolated coal pillars, thereby obtaining a relationship between the development height of the water flowing fractured zones and the data sets of the width of the gasification furnace and the width of the isolated coal pillars in retreating controlled gas injection and underground gasification for strip-face mining; specific gasification furnace width and isolated coal pillar width correspond to specific height of the water flowing fractured zones. For example, for a gasification furnace in a width of 4m and an isolated coal pillar in a width of <com:Math><semantics>5m<annotation encoding="application / x-tex">5m< / annotation>< / semantics>< / com:Math>, height of the water flowing fractured zones is <com:Math><semantics>h1<annotation encoding="application / x-tex">h_1< / annotation>< / semantics>< / com:Math>; for a gasification furnace in a width of 4m and an isolated coal pillar in a width of 5m, height of the water flowing fractured zones is h<com:Sub>2< / com:Sub>; for a gasification furnace in a width of 5m and an isolated coal pillar in a width of 5m, height of the water flowing fractured zones is h<com:Sub>3< / com:Sub>; d. selecting a data combination of the width of the isolated coal pillars and the width of the gasification furnace corresponding to a value of the development height of the water flowing fractured zones that is the closest to but smaller than the limit for the development of the water flowing fractured zones, according to the known limit for the development of the water flowing fractured zones in the study area, in conjunction with the relationship between the development height of the water flowing fractured zones and the data sets of the width of the isolated coal pillars and the width of the gasification furnace in retreating controlled gas injection and underground gasification for strip-face mining, the determined limit for the development of the water flowing fractured zones, and the obtained relationship between the development height of the water flowing fractured zones and the width of the isolated coal pillars and the width of the gasification furnace, and taking the data combination as optimal width of the isolated coal pillars and optimal width of the gasification furnace in retreating controlled gas injection and underground gasification for strip-face mining in the area to be gasified, thereby finishing the design. Example 1 A design method for a width of an isolated coal pillar and a width of a gasification furnace in underground gasification under an overburden aquifer, comprising the following steps: a. determining the maximum height of waterproof coal rock pillars according to the hydrological data and the position of the aquifer in the area to be gasified; b. determining a limit for the development of water flowing fractured zones in the study area to be gasified for coal mining by using the obtained thickness of a protective seam through calculation; C. establishing a numerical model of retreating controlled gas injection and underground gasification for strip-face mining with a numerical simulation method by using the collected hydrogeological data and the mechanical parameters of the rock strata in the area to be gasified, setting the design width of the isolated coal pillars to 4m to 35m inputting 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 and 29m, 30m, 31m, 32m, 33m, 34m, and 35m sequentially into the numerical model, and setting the design width of the gasification furnace to 4m to 35m, i.e., 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, and 35m in the design scheme, calculating the height of the water flowing fractured zones against different values of the width of the isolated coal pillars and the width of the gasification furnace with the established numerical model of retreating controlled gas injection and underground gasification for strip- face mining, thereby determining a relationship between the development height of the water flowing fractured zones and the width of the gasification furnace and the width of the isolated coal pillars in retreating controlled gas injection and underground gasification for strip-face mining; d. finally, selecting the width of the isolated coal pillars and the width of the gasification furnace in retreating controlled gas injection and underground gasification for strip-face mining in the area to be gasified according to the determined limit for the development of the water flowing fractured zones in the study area and the relationship between the development height of the water flowing fractured zone and the width of the isolated coal pillars and the width of the gasification furnace in retreating controlled gas injection and underground gasification for strip- face mining, thereby finishing the design of the width of the isolated coal pillars and the width of the gasification furnace in retreating controlled gas injection and underground gasification for strip-face mining under an overburden aquifer. The specific steps are as follows: step 1: collecting the data of the coal mining area to be gasified, including the hydrogeological data and the drilling location map in the coal mining area in gasification under the overburden aquifer, ascertaining the positions of the overburden aquifer and the confining bed in the area to be gasified, and determining the maximum height <com:Math><semantics>Hwaterproof<annotation encoding="application / x-tex">H_{waterproof}< / annotation>< / semantics>< / com:Math> of the waterproof coal rock pillars according to the position of the aquifer; wherein the waterproof coal rock pillars refer to the coal and rock mass from the upper limit of coal seam mining to the bottom of the water body designed to ensure safe coal mining under the water body; step 2: calculating the thickness <com:Math><semantics>Hprotection<annotation encoding="application / x-tex">H_{protection}< / annotation>< / semantics>< / com:Math> of the protective seam in the area to be gasified with the calculation formula of the thickness of the protective seam reserved for waterproof coal rock pillars as specified in "Specification for Coal Pillar Reservation and Coal Mining under Buildings, Water Bodies, Railroads and Main Roadways" with reference to the geological mining conditions and the lithology of the overlying strata in the area to be gasified, thereby obtaining a limit <com:Math><semantics>Hflowlimit<annotation encoding="application / x-tex">H_{flow\ limit}< / annotation>< / semantics>< / com:Math> for the water flowing fractured zones in the area to be gasified, i.e., <com:Math><semantics>Hflowlimit=Hwaterproof−Hprotection<annotation encoding="application / x-tex">H_{flow\ limit} = H_{waterproof} - H_{protection}< / annotation>< / semantics>< / com:Math>; under gently inclined coal seam and inclined coal seam mining conditions, the thickness of the protective seam in the waterproof and safety coal rock pillars is selected from the following table 1: Table 1 - Thickness of the Protective Seam in the Waterproof and Safety Coal Rock Pillars under Gently Inclined and Inclined Coal Seam Mining Conditions [Image disponible dans le document PDF, Image available in the PDF document] The thickness of the protective seam is calculated according to the above table; specifically, the thickness of the protective seam is calculated according to the lithology of the overlying strata and the mode of occurrence, and is determined as 3A, 4A or 5A, where, "A" is the thickness of the coal seam; for example, the thickness of the protective seam is 6A under the moderate condition of a loose seam without bottom clay soil; in that case, if the thickness of the coal seam is 3m, the thickness of the protective seam is 18m; step 3: establishing a numerical model of retreating controlled gas injection and underground gasification for strip-face mining with ANSYS<com:Sup>TM< / com:Sup> software according to the geological mining conditions, the distribution of the working faces, the ground stress monitoring result, and the profile of mechanical parameter change of the rock at different temperatures in the area to be gasified, dividing the grids, importing the established numerical model of retreating controlled gas injection and underground gasification for strip-face mining into FLAC3D<com:Sup>TM< / com:Sup> and calculating the development height of the water flowing fractured zones; in view of a high-temperature effect of the surrounding rock in the burnt-out zone of underground coal gasification, carrying out mechanical experiments on the compression strength and elastic modulus of the coal seam floor and roof in the area of underground coal gasification to obtain a change law of the compression strength and elastic modulus of the coal seam floor and roof in the area of underground coal gasification with the temperature, as shown in FIG. 2; with reference to the temperature field distribution in the surrounding rock in the burnt-out zone of the test area in retreating controlled gas injection and underground gasification for strip-face mining, as shown in FIG. 3, utilizing Fish language<com:Sup>TM< / com:Sup> to insert the relationship between compression strength and elastic modulus and temperature into the FLAC3D<com:Sup>TM< / com:Sup> model to calculate the height of the water flowing fractured zone, and at the same time, determining the development height of the water flowing fractured zone in underground gasification with a stress analysis method; setting the design width of the isolated coal pillars to 4m to 35m, i.e., 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 and 35m, and setting the design width of the gasification furnace to 4m to 35m, i.e., 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 and 35m in the design scheme, and calculating the height <com:Math><semantics>H1,H2,H3,…,Hn<annotation encoding="application / x-tex">H_1, H_2, H_3, \dots, H_n< / annotation>< / semantics>< / com:Math> of the water flowing fractured zones in retreating controlled gas injection and underground gasification for strip-face mining against different values of the width of the gasification furnace and the width of the isolated coal pillars with the established numerical model according to the simulation scheme; in that way, determining the relationship between the development height of the water flowing fractured zones and the width of the gasification furnace and the width of the isolated coal pillars in retreating controlled gas injection and underground gasification for strip-face mining; step 4: comparing the limit <com:Math><semantics>Hflowlimit<annotation encoding="application / x-tex">H_{flow\ limit}< / annotation>< / semantics>< / com:Math> for the development height of the water flowing fractured zones obtained in the step 2 with the values of the development height <com:Math><semantics>H1,H2,H3,...,Hn<annotation encoding="application / x-tex">H_1, H_2, H_3, ..., H_n< / annotation>< / semantics>< / com:Math> of the water flowing fractured zone obtained in the step 3 against different values of the width of the gasification furnace and the width of the isolated coal pillars in retreating controlled gas injection and underground gasification for strip-face mining, and selecting a value that meets a criterion <com:Math><semantics>Hi≤Hflowlimit<annotation encoding="application / x-tex">H_i \leq H_{flow\ limit}< / annotation>< / semantics>< / com:Math> and is the closest to the limit <com:Math><semantics>Hflowlimit<annotation encoding="application / x-tex">H_{flow\ limit}< / annotation>< / semantics>< / com:Math> as an optimal value <com:Math><semantics>Hi<annotation encoding="application / x-tex">H_i< / annotation>< / semantics>< / com:Math>, and selecting the width of the gasification furnace and the width of the isolated coal pillars in retreating controlled gas injection and underground gasification for strip-face mining according to the optimal value <com:Math><semantics>Hi<annotation encoding="application / x-tex">H_i< / annotation>< / semantics>< / com:Math>, thereby finishing the design of the width of the isolated coal pillars and the width of the gasification furnace in retreating controlled gas injection and underground gasification for strip-face mining under an overburden aquifer.
Claims
1. A method of constructing an underground gasification system under and an overburden aquifer comprising: (i) designing a width of an isolated coal pillar and a width of a gasification furnace for the underground gasification under the overburden aquifer, comprising the following steps: a. determining the maximum height of waterproof coal rock pillars according to the hydrological data and the position of the aquifer in the area to be gasified; b. determining a limit for the development of water flowing fractured zones in a study area to be gasified for coal mining by using the obtained thickness of a protective seam through calculation; c. establishing a numerical model of retreating controlled gas injection and underground gasification for strip-face mining with a numerical simulation method by using collected hydrogeological data and mechanical parameters of the rock strata in the area to be gasified, setting the design width of the isolated coal pillars to 4m to 35m and setting the design width of the gasification furnace to 4m to 35m in the numerical model, combining the width of the gasification furnace and the width of the isolated coal pillars to form a data set and arranging all combined data, calculating the development height of the water flowing fractured zones against different data sets of the width of the isolated coal pillars and the width of the gasification furnace, mapping all the data of the development height of the water flowing fractured zones to the data sets of the width of the gasification furnace and the width of the isolated coal pillars, thereby obtaining a relationship between the development height of the water flowing fractured zones and the data sets of the width of the gasification furnace and the width of the isolated coal pillars in retreating controlled gas injection and underground gasification for strip-face mining; d. selecting a data combination of the width of the isolated coal pillars and the width of the gasification furnace corresponding to a value of the development height of the water flowing fractured zones that is the closest to but smaller than the limit for the development of the water flowing fractured zones, according to the known limit for the development of the water flowing fractured zones in the study area, in conjunction with the relationship between the development height of the water flowing fractured zones and the data sets of the width of the isolated coal pillars and the width of the gasification furnace in retreating controlled gas injection and underground gasification for strip-face mining, the determined limit for the development of the water flowing fractured zones, and the obtained relationship between the development height of the water flowing fractured zones and the width of the isolated coal pillars and the width of the gasification furnace, and taking the data combination as optimal width of the isolated coal pillars and optimal width of the gasification furnace in retreating controlled gas injection and underground gasification for strip-face mining in the area to be gasified, thereby finishing the design; and (ii) . constructing the underground gasification under the overburden aquifer based on the designed widths of the isolated coal pillar and a the gasification furnace for the for installation under the overburden aquifer.
2. The method of constructing an underground gasification system under and an overburden aquifer according to-claim 1, wherein, the specific steps are as follows: step 1: collecting the data of the area to be gasified for coal mining, including the hydrogeological data and the drilling location map in the area for the coal mining area in gasification under the overburden aquifer, ascertaining the positions of the overburden aquifer and the confining bed in the area to be gasified, and determining the maximum height H w a t e r p r o o f H_{waterproof} of the waterproof coal rock pillars according to the position of the aquifer, to ensure that the maximum height H w a t e r p r o o f H_{waterproof} of the waterproof coal rock pillars is smaller than the distance from the coal seam to the aquifer; wherein the waterproof coal rock pillars refer to the coal and rock mass from the upper limit of coal seam mining to the bottom of the water body designed to ensure safe coal mining under the water body; step 2: calculating the thickness H p r o t e c t i o n H_{protection} of the protective seam in the area to be gasified with the calculation formula of the thickness of the protective seam reserved for waterproof coal rock pillars with reference to the geological mining conditions and the lithology of the overlying strata in the area to be gasified, thereby obtaining a limit H f l o w l i m i t H_{flow\ limit} for the water flowing fractured zones in the area to be gasified, and H f l o w _ l i m i t = H w a t e r p r o o f − H p r o t e c t i o n H_{flow\_limit} = H_{waterproof} - H_{protection} ; step 3: establishing a numerical model of retreating controlled gas injection and underground gasification for strip-face mining with ANSYS TM software according to the geological mining conditions, the distribution of the working faces, the ground stress monitoring result, and the profile of mechanical parameter change of the rock at different temperatures in the area to be gasified, dividing the grids, importing the established numerical model of retreating controlled gas injection and underground gasification for strip-face mining into FLAC3D TM and calculating the development height of the water flowing fractured zones; in view of a high-temperature effect of the surrounding rock in the burnt-out zone of underground coal gasification, carrying out mechanical experiments on the rock strata in the study area within the range of 15m distance from the seam floor, 10m distance from the coal seam in the width direction, and 20m distance from the roof to obtain the compression strength and tensile strength of the seam floor, raw coal and roof, a change law of cohesion with temperature within the range of 30°C to 1,000°C in the area to be gasified, displaying the relationship between compression strength, tensile strength and cohesion and temperature with mathematical expressions, utilizing to insert the relationship between compression strength, tensile strength and cohesion and temperature according to the distribution of the surrounding temperature field into the FLAC3D TM model and calculating the height of the water flowing fractured zone, and finally determining the development height of the water flowing fractured zone in underground gasification with a stress analysis method; setting the design width of isolated coal pillars to 4m to 35m and setting the design width of gasification furnace to 4m to 35m, calculating the height H 1 H_1 , H 2 H_2 , H 3 H_3 , ..., H n H_n of the water flowing fractured zones in retreating controlled gas injection and underground gasification for strip-face mining against different values of the width of the gasification furnace and the width of the isolated coal pillars with the established numerical model according to the simulation scheme, thereby determining the relationship between the development height of the water flowing fractured zones and the width of the gasification furnace and the width of the isolated coal pillars in retreating controlled gas injection and underground gasification for strip-face mining; step 4: comparing the limit H f l o w l i m i t H_{flow\ limit} for the development height of the water flowing fractured zones in the area to be gasified with the obtained values H 1 , H 2 , H 3 , . . . , H n H_1, H_2, H_3, ..., H_n of the development height of the water flowing fractured zones and selecting a value that meets H i ≤ H f l o w l i m i t H_i \leq H_{flow\ limit} and is the closest to the limit H f l o w l i m i t H_{flow\ limit} as an optimal value H i H_i , and selecting the width of the gasification furnace and the width of the isolated coal pillars in retreating controlled gas injection and underground gasification for strip-face mining according to the optimal value H i H_i , thereby finishing the design of the width of the isolated coal pillars and the width of the gasification furnace in retreating controlled gas injection and underground gasification for strip-face mining under overburden aquifer.
3. The method of constructing an underground gasification system under and an overburden aquifer according to claim 1, wherein under gently inclined coal seam and inclined coal seam mining conditions, the thickness of the protective seam in the waterproof and safety coal rock pillars is determined according to the following standards: when the thickness of the clay soil at the bottom of the loose seam is greater than the accumulative total mining thickness, then thickness of protective seam is determined as follows: if the lithology of overlying strata is rigid, then the thickness of protective seam is 4 times the thickness of the coal seam; if the lithology of overlying strata is moderate, then the thickness of protective seam is 3 times the thickness of the coal seam; if the lithology of overlying strata is soft, then the thickness of protective seam is 2 times the thickness of the coal seam; if the lithology of overlying strata is very soft, then the thickness of protective seam is 2 times the thickness of the coal seam; when the thickness of the clay soil at the bottom of the loose seam is smaller than the accumulative total mining thickness, then thickness of protective seam is determined as follows: if the lithology of overlying strata is rigid, then the thickness of protective seam is 5 times the thickness of the coal seam; if the lithology of overlying strata is moderate, then the thickness of protective seam is 4 times the thickness of the coal seam; if the lithology of overlying strata is soft, then the thickness of protective seam is 3 times the thickness of the coal seam; if the lithology of overlying strata is very soft, then the thickness of protective seam is 2 times the thickness of the coal seam; when there is no clay soil at the bottom of the loose seam, then thickness of protective seam is determined as follows: if the lithology of overlying strata is rigid, then the thickness of protective seam is 7 times the thickness of the coal seam; if the lithology of overlying strata is moderate, then the thickness of protective seam is 6 times the thickness of the coal seam; if the lithology of overlying strata is soft, then the thickness of protective seam is 5 times the thickness of the coal seam; if the lithology of overlying strata is very soft, then the thickness of protective seam is 4 times the thickness of the coal seam; when the total thickness of the loose seam is smaller than the accumulative total mining thickness, then thickness of protective seam is determined as follows: if the lithology of overlying strata is rigid, then the thickness of protective seam is 6 times the thickness of the coal seam; if the lithology of overlying strata is moderate, then the thickness of protective seam is 5 times the thickness of the coal seam; if the lithology of overlying strata is soft, then the thickness of protective seam is 4 times the thickness of the coal seam; if the lithology of overlying strata is very soft, then the thickness of protective seam is 3 times the thickness of the coal seam.