Artificial geothermal resource energy obtaining method with coal seam in-situ controllable combustion as heat source

Abstract

The invention relates to an artificial geothermal resource energy taking method taking coal seam in-situ controllable combustion as a heat source, which comprises the following steps of: selecting a coal in-situ combustion and artificial heat storage manufacturing area, designing two vertical shafts at two ends of the same horizontal direction of a coal seam, and respectively arranging horizontal wells on a coal seam bottom plate, a coal seam bottom and a coal seam top plate, an oxidizing agent pipeline, a coal seam heat extraction pipeline, a top plate heat extraction pipeline and a bottom plate heat extraction pipeline are laid, a coal seam is ignited after a combustion improver of silane and oxygen is input into a vertical shaft used for setting oxidizing gas injection, the coal seam combustion process is controlled, gas products are continuously monitored and collected, and coal seam circulation heat extraction, top plate circulation heat extraction and bottom plate circulation heat extraction are conducted; by means of the system, earth heat energy is replaced by artificial heat energy, heat energy extraction is controllable, the energy supply requirement is met, safety accidents of traditional coal mining are fundamentally restrained, ash residues are fundamentally prevented from being left in situ, and damage of waste and pollutants to the ground environment is reduced.

Description

Technical Field

[0001] The present invention relates to the field of artificial geothermal resources and mining technology, and in particular to an artificial geothermal resource energy extraction method using in-situ controlled combustion of coal seams as a heat source. Background Art

[0002] In recent years, the development and utilization of geothermal resources has developed rapidly and has become one of the clean and renewable energy sources that countries around the world have focused on developing. Geothermal resources are generally extracted using heat generated by deep energy in the earth. The geothermal resources contained in the depth range of 3 to 10 km in the earth's crust are 30 times the global fossil energy. Geothermal resources are often contained in hot dry rocks. As a green, clean, safe, and efficient high-temperature geothermal energy, hot dry rock resources have huge resources and are widely distributed. They are strategic replacement energy in the future. However, their high-temperature, hard, and dense rock properties require extremely high hydraulic fracturing pressures of 70 to 90 MPa. The expansion and extension of cracks during fracturing are limited, and it is easy to form a single crack with a small range. It is difficult to form a large-scale heat exchange seam network, which reduces the heat exchange efficiency of geothermal mining. In addition, production wells and injection wells need to be connected to the deep heat reservoir formation of more than a kilometer, and the technical conditions for well construction are demanding. The above reasons are the difficulties in achieving the economic and large-scale development and utilization of geothermal resources.

[0003] my country has a resource endowment of rich coal, poor oil and little gas. Coal, as my country's main energy source and important industrial raw material, will not change for a long time in the future. However, my country has a large number of difficult-to-mine coal seams, such as soft coal seams (Praeter coefficient f = 0.1 ~ 0.8), accounting for 53.3% of the total number of coal mines surveyed, and large-angle coal seams (inclination 35° ~ 55°), whose reserves account for about 14.05% of the total coal reserves; thin coal seams (thickness <1.3m) have recoverable reserves of about 6 billion tons, accounting for more than 18% of the total coal reserves in China. my country's basic reserves of relict coal are more than 120 billion tons, and recoverable reserves are about 40 billion tons. In addition, traditional mining methods have forced coal mine production safety to become more severe, with high development costs for deep shaft and tunnel projects, serious losses for enterprises, and backward coal production capacity, resulting in the accelerated closure or abandonment of a large number of coal mines. According to previous studies, coal combustion underground will heat the rock formations within 25 meters. Therefore, the heat energy generated by the in-situ controlled combustion of coal seams can be used to replace the heat energy contained in the earth's interior, thereby realizing artificial geothermal resources. Summary of the invention

[0004] The present invention provides a method for extracting energy from artificial geothermal resources using in-situ controlled combustion of coal seams as a heat source, thereby achieving the replacement of earth thermal energy with artificial thermal energy, making thermal energy extraction controllable, meeting energy supply needs, and fundamentally curbing the occurrence of safety accidents in traditional coal mining, leaving ash and slag in place, and reducing the damage to the ground environment by waste and pollutants.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for obtaining energy from artificial geothermal resources using in-situ controlled combustion of coal seams as a heat source, comprising the following steps:

[0007] S1. Select the coal in-situ combustion and artificial heat storage manufacturing area: the selected coal seams are soft coal seams with a Proton coefficient f = 0.1 to 0.8, coal seams with a steep inclination of 35° to 55°, thin coal seams with a thickness of less than 1.3m, and coal seams that are difficult to use or not mined in closed / waste coal mines for artificial heat storage construction;

[0008] S2. Well construction: two vertical shafts are designed at both ends of the same horizontal direction of the coal seam. Horizontal wells are set on the coal seam floor, coal seam bottom and coal seam roof respectively. One vertical shaft is used to set up the oxidizing gas injection and heat medium output channels, and the other vertical shaft is used to set up the gas product output and heat medium input channels. The roof horizontal well and the bottom horizontal well are respectively separated by a vertical distance of less than 25m from the coal seam;

[0009] S3. Pipeline laying: arranging an oxidant pipeline and a circulating medium pipeline, wherein the oxidant pipelines are respectively extended from two vertical shafts to the coal seam for communication, and the oxidant pipelines in the coal seam are screen pipes;

[0010] The circulating medium pipeline includes: coal seam heat extraction pipelines extending from two vertical shafts to the coal seam for communication;

[0011] The roof heat extraction pipelines extend from two vertical shafts to the roof within 25m of the coal seam;

[0012] The bottom plate heat extraction pipelines extend from two vertical shafts to the bottom plate within 25m from the coal seam, and at the same time, horizontal pipelines are connected in parallel at intervals of 25m along the inclination direction of the coal seam;

[0013] The coal seam heat extraction pipeline, the top plate heat extraction pipeline and the bottom plate heat extraction pipeline are all filled with circulating heat extraction medium;

[0014] S4, ignite the coal seam: inject a combustion-supporting agent of silane and oxygen into the vertical shaft for setting up the oxidizing gas injection, and then ignite the coal seam. When the temperature of the coal seam is stably higher than 300°C, introduce air or oxygen-enriched air to ensure continuous and stable combustion of the coal seam;

[0015] S5. Coal seam combustion process control: using the oxidant pipeline in the coal seam to control the coal seam combustion rate and combustion direction;

[0016] S6. Continuously monitor and collect gas products: When the test results show that CO 2 When the volume fraction is lower than 20% and fluctuates, increase the oxygen concentration and oxygen flow rate. The oxygen concentration is increased to 80% at most, and the oxygen flow rate is increased to the point where CO 2The volume fraction will not be increased above 20%;

[0017] S7. Coal seam circulation heat extraction: The oxidant pipeline buried in the coal seam is set 1 to 25 meters below the left side of the coal seam heat extraction pipeline in the coal seam, so that the circulating medium pipeline is in the high-temperature coal flame area;

[0018] S8. Circulation heating of roof and bottom plates: Roof heating pipes and bottom plate heating pipes are set less than 25m away from the roof and bottom plates of the coal seam. The roof heating pipes and bottom plate heating pipes are on the same plumb line, and a circulating medium pipe is set at intervals less than 25m.

[0019] Furthermore, when igniting the coal seam, the ignition of the steeply inclined coal seam starts from the lowest level area of ​​the coal seam and gradually ignites along the inclination direction of the coal seam toward the higher level area.

[0020] Furthermore, when igniting the coal seam, the thick coal seam with a thickness of ≥1.3m is ignited from the bottom of the coal seam and gradually burns upward.

[0021] Furthermore, in step S5, the combustion rate is controlled by changing the oxygen concentration and the oxidant flow rate, and the combustion direction is controlled by changing the screen arrangement of the oxidant pipeline in the coal seam.

[0022] Furthermore, the circulating medium pipeline in the coal seam is a spiral bend pipe.

[0023] Furthermore, in the coal seam circulating heat extraction, the flow direction of the circulating heat extraction medium is opposite to the combustion direction of the heat source center point along the coal seam.

[0024] Furthermore, in the coal seam circulating heat extraction, the circulating heat extraction medium in the pipeline is water or an organic working fluid. When the top plate and bottom plate temperatures are both 60-90°C, working fluid R601a is used, when the temperature is 90-130°C, working fluid R134a is used, for temperatures between 130-200°C, working fluid R290 is used, and when the temperature is higher than 200°C, water is used.

[0025] Furthermore, in the top plate and bottom plate circulating heat extraction, the circulating medium pipelines in the top plate and bottom plate are spiral bent pipes.

[0026] Furthermore, in the top plate and bottom plate circulation heat extraction, the circulating heat extraction medium in the pipeline is water or an organic working fluid. When the temperatures of the top plate and the bottom plate are both 60-90°C, the working fluid R601a is used, when the temperature is 90-130°C, the working fluid R134a is used, when the temperature is 130-200°C, the working fluid R290 is used, and when the temperature is higher than 200°C, water is used.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) The heat energy generated by the in-situ controlled combustion of coal seams can replace the heat energy contained in the earth's interior to realize artificial geothermal resources, make full use of the coal resources left over from difficult-to-mine, closed / abandoned mines, fundamentally curb the occurrence of safety accidents in traditional coal mining, leave ash and slag in place, and reduce the damage of waste and pollutants to the ground environment;

[0029] 2) Artificially control the coal seam combustion process to replace the earth's thermal energy with artificial thermal energy, make thermal energy extraction controllable, meet energy supply needs, and avoid the barriers of complex well construction technology and hydraulic fracturing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the pipeline setting position structure of the present invention.

[0031] Figure 2 It is a schematic diagram of the combustion direction of the steeply inclined coal seam described in the present invention.

[0032] Figure 3 It is a schematic diagram of the combustion direction structure of the thick coal seam according to the present invention.

[0033] Figure 4 It is a schematic diagram of controlling the coal seam combustion direction by introducing oxidant flow according to the present invention.

[0034] Figure 5 It is a schematic diagram of changing the oxidant injection direction to control the coal seam combustion direction according to the present invention.

[0035] Figure 6 It is a schematic diagram of the heat extraction process of the coal seam heat extraction pipeline of the present invention.

[0036] Figure 7 It is a schematic diagram of the arrangement of the top plate, bottom plate and heat extraction pipelines in the coal seam according to the present invention.

[0037] In the figure: 1. Roof 2. Coal seam 3. Floor 4. Roof heat pipe 5. Coal seam heat pipe 6. Oxidant pipe 7. Floor heat pipe 8. Shaft a 9. Shaft b 10. Screen pipe 11. Spiral bend 12. High-angle coal seam 13. Coal seam ignition start area DETAILED DESCRIPTION

[0038] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings:

[0039] See Figure 1 , is a schematic diagram of the pipeline arrangement structure of the present invention. The present invention provides an artificial geothermal resource energy extraction method using coal seam in-situ controlled combustion as a heat source, comprising the following steps:

[0040] S1. Select coal in-situ combustion and artificial heat storage manufacturing area: the selected coal seam 2 is a soft coal seam 2 with a Proctor coefficient f=0.1~0.8, a steeply inclined coal seam 12 with an inclination of 35°~55°, a coal seam 2 with a thickness of less than 1.3m, and a closed / waste coal mine or other difficult-to-use and unmined coal seam 2 for artificial heat storage construction.

[0041] S2. Well construction: two vertical shafts are designed at both ends of the same horizontal direction of coal seam 2, one of which is used as an oxidizing gas injection and heat medium output channel; the other vertical shaft is used as a gas product output and heat medium input channel. Three horizontal wells are set up, respectively arranged at the coal seam floor 3, the coal seam bottom, and the coal seam roof 1. Since the temperature influence range of coal seam 2 during combustion is about 25m, the horizontal wells on the roof 1 and the bottom 3 are set within a vertical distance of 25m from the coal seam 2.

[0042] S3. Pipeline laying: The whole system has four types of pipelines. The first type of pipeline is the oxidant pipeline 6, which extends from the shaft a8 and the shaft b9 to the coal seam 2. The oxidant injection pipeline in the coal seam 2 is a screen pipe 10, in order to allow the oxidizing gas to enter the coal seam 2. The second type of pipeline is the coal seam 2 heat extraction pipeline 5, which extends from the shaft a8 and the shaft b9 to the coal seam 2. This pipeline is a high-temperature resistant metal pipeline, and the heat extraction medium is introduced into the fully enclosed pipeline. The third pipeline is the roof extraction pipeline 5. The heat pipe 4 is respectively extended from the vertical shaft a8 and the vertical shaft b9 to the top plate 1 within 25m of the coal seam 2, and the heat medium is passed into the pipe. At the same time, three groups of pipes are connected in parallel at intervals of 25m along the inclination direction of the coal seam 2; the fourth type of pipe is the bottom plate heat pipe 7, which is respectively extended from the vertical shaft a8 and the vertical shaft b9 to the bottom plate 3 within 25m of the coal seam 2, and the heat medium is passed into the pipe. At the same time, three groups of pipes are connected in parallel at intervals of 25m along the inclination direction of the coal seam 2, such as Figure 1 shown.

[0043] S4, ignite coal seam 2: inject silane and 90% oxygen into the shaft a8 to ignite coal seam 2. When the temperature of coal seam 2 is stably above 300°C, it means that coal seam 2 is completely ignited. At this time, introduce air or oxygen-enriched air to make coal seam 2 burn continuously and stably.

[0044] like Figure 2As shown, when igniting the steeply inclined coal seam 12, it is necessary to start igniting from the lowest level area of ​​the coal seam 2, which is the starting ignition area 13 of the coal seam 2, and gradually ignite along the inclination direction of the coal seam 2 toward the high level area. When the coal seam 2 in the low level area burns, the high level coal is preheated by high temperature, which helps the high level coal seam 2 to burn more quickly and completely in the later stage. After the low level coal seam 2 burns, the ash in the combustion zone is left at the bottom and will not cover the surface of the upper coal seam 2, making the high level coal seam 2 easier to ignite. In addition, after the low level coal seam 2 is exhausted, the high level will gradually collapse to form a large number of macro cracks, making it easier for the oxidant to migrate in the coal seam 2, thereby improving the combustion efficiency of the coal seam 2.

[0045] like Figure 3 As shown, when igniting a thick coal seam 2, it is necessary to burn from the bottom of the coal seam 2 gradually to the upper part. This combustion process is similar to the combustion process of the steeply inclined coal seam 12. In addition to preheating the high-level coal seam 2 in advance, the ash is left in the lower part, and the upper coal seam 2 collapses to form an oxidant migration and diffusion channel.

[0046] S5, coal seam 2 combustion process control: Figure 4 As shown, the combustion rate and direction of the coal seam 2 are controlled by using the oxidant pipe 6 in the coal seam 2, as shown in FIG. Figure 4 As shown, the combustion rate can be controlled by changing the oxygen concentration and the oxidant flow rate. For example, when the same flow rate is injected into the coal seam 2, the combustion rate of the coal seam 2 is faster when the oxygen concentration is 50% than when the oxygen concentration is 21%; when the same oxygen concentration is injected into the coal seam 2, the combustion rate of the coal seam 2 is faster when the oxygen injection rate is 400Nm3 / h than when the oxygen injection rate is 200Nm3 / h; Figure 5 As shown, with the coal seam inclination 2 as the positive x-axis and the coal seam 2 strike as the positive y-axis, the oxidant injection pipeline releases oxidant perpendicular to the x-axis of the coal seam 2, and the combustion direction moves along the positive x-axis. When the injection pipeline is less than 90°, such as 60°, it turns to the negative y-axis. When the injection pipeline is greater than 90°, it turns to the positive y-axis. The combustion direction is controlled by changing the arrangement of the screen pipe 10 of the oxidant pipeline 6 in the coal seam 2.

[0047] S6. Continuously monitor and collect gas products: When the test results show that CO 2 When the volume fraction is lower than 20% and fluctuates, it indicates that the combustion stability of coal seam 2 is weakened, and the oxygen concentration and oxygen flow rate need to be increased. The oxygen concentration can be increased to 80% and the oxygen flow rate can be increased to the point where CO 2 The volume fraction does not increase any more above 20%.

[0048] S7, Coal Seam 2 Circulation Heat Extraction: Figure 6As shown, the distance between the oxidant pipeline 6 buried in the coal seam 2 and the coal seam 2 heat extraction pipeline 5 of the circulating medium pipeline is close, and the oxidant pipeline 6 is located 1m below the left of the coal seam 2 heat extraction pipeline 5 of the circulating medium pipeline, so that the coal seam 2 heat extraction pipeline 5 of the circulating medium pipeline is in the high-temperature flame zone of the coal; the circulating medium pipeline in the coal seam 2 is a spiral bend 11, which increases the heat exchange area; the flow direction of the circulating heat extraction medium is opposite to the combustion direction of the heat source center point along the coal seam 2;

[0049] The heat medium circulating in the pipeline is water or organic working fluid. The organic working fluid includes R290, R134a, R600a, R600, and R601a. ​​When the temperature of the top plate 1 and the bottom plate 3 are both 60-90°C, the working fluid R601a is used, and the temperature is 90-130°C. The working fluid R134a is used. For the temperature of 130-200°C, the working fluid R290 is used, and when the temperature is higher than 200°C, water is used.

[0050] S8, top plate 1 and bottom plate 3 circulate heat: Figure 7 As shown, a heat extraction pipeline is set at a distance of less than 25m from the coal seam roof 1 and the bottom plate 3, the roof heat extraction pipeline 4 and the bottom plate heat extraction pipeline 7 are on the same plumb line, and a circulation pipeline is set at intervals of less than 25m to ensure that the heat within the combustion influence range of the coal seam 2 can be extracted by the circulating heat extraction medium, and at the same time form an artificial cooling layer to prevent high-temperature artificial heat storage from affecting distant rock formations; the circulating medium pipelines in the roof 1 and the bottom plate 3 are spiral bends 11 to increase the heat exchange area;

[0051] The heat medium circulating in the pipeline is water or organic working fluid. The organic working fluid includes R290, R134a, R600a, R600, and R601a. ​​When the temperature of the top plate 1 and the bottom plate 3 is 60-90°C, the working fluid R601a is used, and the temperature is 90-130°C. The working fluid R134a is used. For the temperature of 130-200°C, the working fluid R290 is used, and when the temperature is higher than 200°C, water is used.

[0052] The above embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the above embodiments. The methods used in the above embodiments are conventional methods unless otherwise specified.

Claims

1. A method for obtaining energy from artificial geothermal resources using in-situ controlled combustion of coal seams as a heat source, characterized in that: The steps include: S1. Select the coal in-situ combustion and artificial heat storage manufacturing area: the selected coal seams are soft coal seams with a Proton coefficient f = 0.1 to 0.8, coal seams with a steep inclination of 35° to 55°, thin coal seams with a thickness of less than 1.3m, and coal seams that are difficult to use or not mined in closed / waste coal mines for artificial heat storage construction; S2. Well construction: two vertical shafts are designed at both ends of the same horizontal direction of the coal seam. Horizontal wells are set on the coal seam floor, coal seam bottom and coal seam roof respectively. One vertical shaft is used to set up the oxidizing gas injection and heat medium output channels, and the other vertical shaft is used to set up the gas product output and heat medium input channels. The roof horizontal well and the bottom horizontal well are respectively separated by a vertical distance of less than 25m from the coal seam; S3. Pipeline laying: arranging an oxidant pipeline and a circulating medium pipeline, wherein the oxidant pipelines are respectively extended from two vertical shafts to the coal seam for communication, and the oxidant pipelines in the coal seam are screen pipes; The circulating medium pipeline includes: coal seam heat extraction pipelines extending from two vertical shafts to the coal seam for communication; The roof heat extraction pipelines extend from two vertical shafts to the roof within 25m of the coal seam; The bottom plate heat extraction pipelines extend from two vertical shafts to the bottom plate within 25m from the coal seam, and at the same time, horizontal pipelines are connected in parallel at intervals of 25m along the inclination direction of the coal seam; The coal seam heat extraction pipeline, the top plate heat extraction pipeline and the bottom plate heat extraction pipeline are all filled with circulating heat extraction medium; S4, ignite the coal seam: inject a combustion-supporting agent of silane and oxygen into the vertical shaft for setting up the oxidizing gas injection, and then ignite the coal seam. When the temperature of the coal seam is stably higher than 300°C, introduce air or oxygen-enriched air to ensure continuous and stable combustion of the coal seam; S5. Coal seam combustion process control: using the oxidant pipeline in the coal seam to control the coal seam combustion rate and combustion direction; S6. Continuously monitor and collect gas products: When the test shows that the CO2 volume fraction is lower than 20% and fluctuates, increase the oxygen concentration and oxygen flow rate. The oxygen concentration is increased to a maximum of 80%, and the oxygen flow rate is increased until the CO2 volume fraction in the gas product is higher than 20%. S7. Coal seam circulation heat extraction: The oxidant pipeline buried in the coal seam is set 1 to 25 meters below the left side of the coal seam heat extraction pipeline in the coal seam, so that the circulating medium pipeline is in the high-temperature coal flame area; S8. Circulation heating of roof and bottom plates: Roof heating pipes and bottom plate heating pipes are set less than 25m away from the roof and bottom plates of the coal seam. The roof heating pipes and bottom plate heating pipes are on the same plumb line, and a circulating medium pipe is set at intervals less than 25m.

2. The method for obtaining energy from artificial geothermal resources using in-situ controlled combustion of coal seams as a heat source according to claim 1, characterized in that: When the coal seam is ignited, the ignition of the steeply inclined coal seam starts from the lowest level area of ​​the coal seam and gradually ignites along the inclination direction of the coal seam toward the higher level area.

3. The method for obtaining energy from artificial geothermal resources using in-situ controlled combustion of coal seams as a heat source according to claim 1, characterized in that: When the coal seam is ignited, a thick coal seam with a thickness of ≥1.3 m is ignited from the bottom of the coal seam and gradually burns upward.

4. The method for obtaining energy from artificial geothermal resources using in-situ controlled combustion of coal seams as a heat source according to claim 1, characterized in that: In step S5, the combustion rate is controlled by changing the oxygen concentration and the oxidant flow rate, and the combustion direction is controlled by changing the screen arrangement of the oxidant pipeline in the coal seam.

5. The method for obtaining energy from artificial geothermal resources using in-situ controlled combustion of coal seams as a heat source according to claim 1, characterized in that: The circulating medium pipeline in the coal seam is a spiral bent pipe.

6. The method for obtaining energy from artificial geothermal resources using in-situ controlled combustion of coal seams as a heat source according to claim 1, characterized in that: In the coal seam circulating heat extraction, the flow direction of the circulating heat extraction medium is opposite to the combustion direction of the heat source center point along the coal seam.

7. The method for obtaining energy from artificial geothermal resources using in-situ controlled combustion of coal seams as a heat source according to claim 1, characterized in that: In the coal seam circulating heat extraction, the circulating heat extraction medium in the pipeline is water or an organic working fluid. When the top plate and bottom plate temperatures are both 60-90°C, working fluid R601a is used, when the temperature is 90-130°C, working fluid R134a is used, when the temperature is 130-200°C, working fluid R290 is used, and when the temperature is higher than 200°C, water is used.

8. The method for obtaining energy from artificial geothermal resources using in-situ controlled combustion of coal seams as a heat source according to claim 1, characterized in that: In the top plate and bottom plate circulation heat extraction, the circulating medium pipelines in the top plate and bottom plate are spiral bent pipes.

9. The method for obtaining energy from artificial geothermal resources using in-situ controlled combustion of coal seams as a heat source according to claim 1, characterized in that: In the top plate and bottom plate circulation heat extraction, the circulating heat extraction medium in the pipeline is water or an organic working fluid. When the top plate and bottom plate temperatures are both 60-90°C, working fluid R601a is used, when the temperature is 90-130°C, working fluid R134a is used, when the temperature is 130-200°C, working fluid R290 is used, and when the temperature is higher than 200°C, water is used.

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