High-temperature steam in-situ coal leaching hydrogen production and waste residue in-situ metal leaching method

Abstract

The invention discloses a high-temperature steam in-situ coal leaching hydrogen production and waste residue in-situ metal mining method, and belongs to the technical field of coal underground in-situ hydrogen production and resource comprehensive utilization. The method comprises the following steps: firstly, injecting high-temperature and high-pressure steam into a target coal seam through a ground or underground drill hole, enabling the steam to seep in a coal seam fracture network subjected to fracturing transformation by utilizing pumping and injecting pressure difference, and carrying out pyrolysis and gasification reaction with coal to generate a combustible gas-liquid mixture taking hydrogen as a main component; after the product is extracted and separated, hydrogen and other resources are recycled, and coke is retained in underground supporting overburden strata. And then, according to the porous waste residue ore deposit rich in metal formed after gasification, adaptive in-situ leaching liquid is injected through original or newly-arranged drill holes, and valuable metal in the porous waste residue ore deposit is dissolved and recycled. According to the invention, direct ignition and oxygen injection combustion of traditional underground gasification are avoided, the problems of easy flameout, unstable gas production, low heat value and the like are solved, and meanwhile, clean hydrogen production of coal and green collaborative mining of associated metal resources are realized.

Description

Technical Field

[0001] This invention relates to the field of underground in-situ hydrogen production and comprehensive resource utilization technology, specifically to a method for producing hydrogen from coal by high-temperature steam leaching and extracting metals from waste residue by leaching. Background Technology

[0002] Traditional underground coal mining faces problems such as roof collapse, water inrush, and gas explosions. In particular, traditional coal mining methods face significant challenges, especially for deep, steeply inclined, and thin coal seams, which are difficult to mine. These challenges include difficulties in ensuring safety, serious environmental damage, low efficiency, and high costs.

[0003] Underground coal gasification (UCG), also known as "gasification mining" or "chemical mining," refers to the controlled combustion of coal under in-situ conditions using specific technologies. Through coal pyrolysis and chemical reactions with oxygen and steam, combustible gases such as CH4, H2, and CO are produced. Compared to traditional coal mining methods, UCG integrates shaft construction, coal mining, and conversion, eliminating many traditional development stages. This not only saves time, costs, and resources but also avoids environmental problems such as gangue dumping and dust pollution, while mitigating potential disasters like underground accidents and casualties that can occur with traditional coal mining.

[0004] However, underground coal gasification suffers from problems such as mid-process flameout and production stoppage due to roof collapse and water inrush. Currently, UCG technology faces challenges including difficulty in ignition within the combustion gasifier, easy flameout, difficulty in combustion control, unstable gas production, low calorific value of the produced gas, low gas production rate, and high carbon dioxide content in the produced gas. Statistics show that most UCG demonstration projects in the past 30 years have been forced to shut down due to these reasons, severely hindering the large-scale promotion and application of UCG. The main reasons for "easy flameout, difficult combustion control, and unstable gas production" are related to roof fractures in the combustion chamber, rock strata movement, and water inrush. The fundamental reason for "low calorific value of the produced gas, low gas production rate, and high carbon dioxide content" is related to direct oxygen injection combustion within the coal seam. Oxygen easily reacts with gasification products (CH4, H2, and CO) to generate carbon dioxide and occupies the gasification channel, ultimately leading to high carbon dioxide content, low calorific value, and low gas production rate in the produced gas. Ultimately, "coal combustion" is the main factor inducing these problems.

[0005] In addition, coal often contains a variety of valuable metal elements, and traditional coal mining or existing UCG technology does not pay enough attention to the recycling and utilization of these resources, resulting in resource waste.

[0006] Therefore, there is an urgent need for a new underground conversion technology that can avoid direct combustion, achieve stable and efficient hydrogen production, and simultaneously recover associated resources from coal. Summary of the Invention

[0007] The purpose of this invention is to provide a method for producing hydrogen from coal by high-temperature steam leaching and for mining metals from waste residue by leaching, so as to solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution.

[0009] A method for producing hydrogen from coal by high-temperature steam leaching and mining metals from its waste residue includes the following steps: S1, drilling construction: This is divided into two scenarios: surface construction and underground roadway construction. At the surface, at least two parallel boreholes are drilled into the same coal seam along a near-vertical direction. In the roadway, at least two parallel boreholes are drilled into the same coal seam in the direction of the coal seam. The boreholes are initially used as fracturing boreholes and later as steam injection holes and hydrogen extraction holes, respectively. After the drilling is completed, borehole screens need to be installed as inlet and outlet channels for steam and product gases.

[0010] S2. Fracturing and Permeability Enhancement: Pulse fracturing equipment is deployed to fracture and enhance the permeability of the coal seam using injection holes and extraction holes, respectively, so as to form an interconnected fracture network in the area between the boreholes and enhance the in-situ leaching effect.

[0011] S3. Steam Immersion Facility Installation: A steam generator is installed, with its inlet connected to the gas injection pipeline and water injection pipeline, and its outlet connected to the steam pipeline. The steam pipeline is connected to the coal seam fracture network through a borehole screen. A sealing device is installed on the outside of the borehole screen to form an effective seal at the bottom of the borehole. The gas injection pipeline is equipped with a check valve, a flame-retardant valve, and a flow sensor. Temperature and pressure sensors are installed inside the steam generator. A pressure control valve is installed on the steam pipeline. The bottom of the extraction pipeline in the extraction hole is connected to the coal seam fracture network, and the upper part leads to the ground.

[0012] S4. Reaction gas injection: Reaction gas is introduced into the steam generator and / or electrical energy is used to directly or indirectly generate high-temperature and high-pressure steam; through pressure control technology, the high-temperature and high-pressure steam in the steam generator is discharged into the steam pipeline, and the high-temperature steam flows into the coal seam fracture network through the perforated screen at the end of the steam pipeline.

[0013] S5. Product Gas Extraction: Utilizing the injection-extraction pressure difference, high-temperature steam is forced to flow from the injection hole to the extraction hole along the coal seam fracture network. During this process, the high-temperature steam interacts with the coal, causing the coal to undergo pyrolysis and gasification. The hydrogen, tar, and other gases produced by pyrolysis and gasification flow along the pressure gradient direction within the fracture network to the extraction hole and are further extracted to the surface.

[0014] S6. Product Separation and Recovery: Separation and recovery devices are set up to separate tar, waste gas, etc., and to separate and recover hydrogen, methane and other fuels based on multi-stage separation technology.

[0015] S7. Cooling of waste slag deposit: Desalination room temperature cooling water is injected into the coal seam waste slag deposit formed after gasification in steps S1-S6 to reduce the temperature of the coal seam after pyrolysis, providing conditions for subsequent leaching of valuable metals with water-based leaching solution.

[0016] S8. Injection of leaching solution: Inject a suitable leaching solution into the coal seam waste slag deposit after it has been cooled and treated in step S7 to dissolve the valuable metals therein and form a leaching solution.

[0017] S9. Extraction of leaching solution: The leaching solution is extracted from the waste slag deposit for metal recovery.

[0018] As a further aspect of the present invention: in step S1, when drilling in the roadway, the drilling direction is usually perpendicular to the roadway wall, and when drilling on the ground, the drilling direction is usually vertically downward; the drilling depth is usually equal to the local average burial depth of the target coal seam and cannot penetrate the bottom plate of the coal seam; the distance between the boreholes is usually not less than 10 meters.

[0019] As a further aspect of the present invention: in step S2, the fracturing and permeability enhancement method is pulsed hydraulic fracturing; during fracturing, the fracture distribution is assessed by means of microseismic monitoring, and after fracturing, the connectivity of the fracture network between boreholes is assessed by unidirectional water injection.

[0020] As a further aspect of the present invention: in step S3, the steam generating device is a surface steam boiler, an underground roadway steam boiler, or a borehole-type steam boiler installed in a borehole; when the steam boiler is located on the surface or in a roadway, the steam pipeline is insulated; when a borehole-type steam boiler is used, it is installed above the coal seam and within 0-50 meters of the gasified coal seam; the pipeline system is equipped with flow, temperature, and pressure sensors, as well as check valves and flame-retardant valves.

[0021] As a further aspect of the present invention: in step S4, the method of generating high-temperature and high-pressure steam is as follows: hydrogen and oxygen are injected into the steam generator, and they are mixed and burned to generate high temperature, while the injected water is heated to generate high-temperature and high-pressure steam; or, the injected water is heated by electric energy to generate high-temperature and high-pressure steam; the temperature of the high-temperature and high-pressure steam is 300-1000℃, and the pressure is controlled according to the coal seam conditions and the gas injection volume requirements.

[0022] As a further aspect of the present invention: in step S5, the injection-extraction pressure difference is achieved by controlling the positive pressure of the injection hole steam and / or the negative pressure of the extraction hole, using positive pressure displacement, negative pressure suction, or a combination of both.

[0023] As a further aspect of the present invention: in step S6, the separation and recovery includes: separating tar by gravity sedimentation and filtration, removing moisture by adsorption drying, and purifying hydrogen by pressure swing adsorption.

[0024] As a further aspect of the present invention: In step S7, under the pressure environment of the coal seam waste ore deposit, the final cooling temperature should be such that the water is in a liquid state, and should not be too low, so as to improve the efficiency of subsequent leaching chemical reaction.

[0025] As a further aspect of the present invention: in step S8, the coal seam waste slag deposit is coke and semi-coke with a porous structure; the leaching solution is selected according to the type of target metal in the waste slag, including acidic or alkaline leaching solution systems.

[0026] As a further aspect of the present invention: in step S9, the extraction of the leachate adopts a combination of negative pressure extraction and positive pressure displacement, utilizing existing gasification stage extraction wells or newly established extraction wells.

[0027] Compared with the prior art, the beneficial effects of the present invention are: 1. It abandons the traditional UCG mode of directly igniting coal seams and adopts high-temperature steam ground immersion, which does not require ignition and effectively avoids the problem of flameout caused by unstable combustion, roof collapse, and water inrush. The steam can continuously contact the coal through the rock strata fissures, and the reaction process is mild and controllable, and the gas production composition and rate are more stable.

[0028] 2. High hydrogen yield and high product calorific value: Using high-temperature steam as the heat source and reaction medium, the main processes are coal pyrolysis and water-gas reaction, which directly generate hydrogen. This greatly inhibits the generation of carbon dioxide, making the product gas mainly hydrogen with a high calorific value, which is more conducive to subsequent purification and utilization.

[0029] 3. Successful sequential extraction of hydrogen and metal resources: Innovatively combining in-situ hydrogen production from coal with in-situ metal leaching from waste residue, within a single well network and process system, energy substances (hydrogen) and mineral resources (metals) in coal are extracted sequentially, improving the comprehensive utilization efficiency of coal resources.

[0030] 4. In the hydrogen production process, the carbon is primarily stored underground in the form of solid coke, reducing greenhouse gas emissions. In-situ leaching of metals avoids the environmental problems of stripping and waste rock dumping associated with traditional ore mining.

[0031] 5. Strong adaptability: It is particularly suitable for resource development in deep, steeply inclined, and low-permeability coal seams, breaking through the limitations of traditional mining technology and expanding the scope of coal resource utilization. Attached Figure Description

[0032] Figure 1 This is a process flow diagram of the method described in this invention.

[0033] Figure 2 This is a schematic diagram of a ground-drilled (well) type high-temperature steam leaching method for producing hydrogen from coal according to the present invention.

[0034] Figure 3This is a schematic diagram of a ground-drilled (well) type high-temperature steam leaching coal hydrogen production extraction and injection unit according to the present invention.

[0035] Figure 4 This is a schematic diagram of the structure of the drilled steam furnace described in this invention.

[0036] Figure 5 This is a schematic diagram of a tunnel-type high-temperature steam leaching coal hydrogen production method according to the present invention.

[0037] Figure 6 This is a top view of a tunnel-type high-temperature steam leaching coal hydrogen production method according to the present invention.

[0038] In the diagram: 1. Coal seam; 2. Coal seam floor; 3. Injection hole; 4. Extraction hole; 5. Drilled steam boiler; 6. Drilled screen pipe; 7. Pulse seam mesh; 8. Coal seam roof; 9. Water injection pipeline; 10. Gas injection pipeline; 11. Extraction pipeline; 12. Surface gas injection station; 13. Surface gas gathering station; 14. Hydrogen recovery pipeline; 15. Surface water injection station; 16. Hydrogen-oxygen combustion chamber; 17. Temperature sensor; 18. Pressure sensor; 19. Hydrogen pipeline; 20. Oxygen pipeline; 21. Flow sensor; 22. Check valve; 23. Flame retardant valve; 24. Steam buffer chamber; 25. Pressure control valve; 26. Sealing device; 27. Ignition device; 28. Steam generator; 29. ​​Steam pipeline; 30. Roadway. Detailed Implementation

[0039] The technical solution of this application will be further described in detail below with reference to specific embodiments.

[0040] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0041] Please see Figure 1 A method for producing hydrogen from coal by high-temperature steam leaching and mining metals from waste residue by leaching includes the following steps: S1. Drilling and injection; S2. Fracturing and permeability enhancement; S3. Installation of steam leaching facilities; S4. Injection of reaction gas; S5. Extraction of product gas; S6. Separation and recovery of product; S7. Cooling of waste residue deposit; S8. Injection of leaching solution; S9. Extraction of leaching solution.

[0042]

Example 1

[0043] This embodiment relies on the No. 2 coal seam of a certain coal mine in Inner Mongolia. This coal seam is a nearly horizontal coal seam with an inclination angle of 5°-8°, an average burial depth of 580 m, a coal seam thickness of 4.8-6.2 m, and an average thickness of 5.5 m. It belongs to a low-permeability coal seam (permeability 0.08-0.8 mD). The coal quality is long flame coal, with a fixed carbon content of 65%, a volatile matter content of 32%, and a sulfur content of 0.5%. It has excellent pyrolysis and gasification characteristics and is suitable for carrying out in-situ gasification hydrogen production operations by ground drilling. The project takes patented technology as the core, designs a production system for high-temperature steam in-situ leaching of coal to produce hydrogen and in-situ leaching of metals from its waste residues, and realizes the efficient conversion and clean utilization of coal resources by precisely controlling the parameters of each step.

[0044] Step S1: Construction of injection and extraction boreholes.

[0045] Combined with the inclination angle and burial depth of coal seam 1, the borehole depth is set to 579 m to ensure that the end of the borehole completely penetrates coal seam 1, and the borehole depth shall not exceed the coal seam floor 2, as Figure 2 shown. Layout the injection and extraction units as Figure 3 shown. Each injection and extraction unit includes 4 injection holes 3 and 1 extraction hole 4. The injection holes 3 and extraction holes 4 are arranged alternately, with a borehole spacing of 30 m. The borehole diameter is selected as 0.15 m to meet the size requirements of the borehole-type steam furnace 5. Select a suitable drilling rig for ground drilling, lower a special heat-insulating casing, and inject cement for well cementing. After completion of the well, install a Φ150 mm borehole screen pipe 6 at the end of the borehole (575-579 m). The pore diameter of the screen pipe is 5 mm to ensure smooth steam injection and gas extraction. During construction, a logging-while-drilling tool is used to monitor the borehole trajectory in real time, and the azimuth deviation is controlled within ±2° to avoid borehole misalignment affecting subsequent connection. After the borehole is completed, check the integrity of the casing and the quality of well cementing through ultrasonic imaging logging to ensure no channeling or leakage, and use a clear water circulation test to check the borehole smoothness.

[0046] Step S2: Fracturing to increase permeability.

[0047] Arrange pulse fracturing equipment on the ground. Each set includes a high-pressure water injection pump with a rated pressure of 30 MPa, a pulse generator with adjustable frequency, and a

[0049] fracturing fluid storage tank of 60 m. Combined with the low-permeability characteristics of the coal seam, set the water pressure to 30 MPa and the pulse frequency to 30 Hz. The single-hole fracturing duration is not less than 30 minutes. Through the periodic change of pulse pressure, promote the cracks to extend to adjacent boreholes to form a pulse fracture network 7. After fracturing, wait for 24 hours, and use the water injection method to test the connectivity of the fractured cracks. Inject clear water into the injection hole 3 at a constant speed, with the pressure stabilized at 4 MPa, and at the same time measure the water output of the extraction hole 4. When the water output in the extraction hole 4 reaches more than 80% of the injection volume, it is determined that the connection is qualified.

[0048] Step S3: Installation of steam in-situ leaching facilities.

[0049] Considering the coal seam burial depth and operation safety, the borehole steam furnace 5 is arranged underground, 10 m above the coal seam roof 8. The rated power of a single borehole steam furnace 5 is 1000 kW, the design pressure is 25 MPa, and the temperature resistance is 1200 °C. It can generate steam at 300 - 1000 °C to meet the heat demand. The structural schematic diagram of the borehole steam furnace 5 is as shown in Figure 4 shown. Its main structure includes a water injection pipeline 9, a hydrogen pipeline 19, and an oxygen pipeline 20. Flow sensors 21, check valves 22 (to prevent gas backflow), and flame retardant valves 23 (for fire and explosion prevention) are sequentially installed on the pipelines. A hydrogen-oxygen combustion chamber 16 is also designed, and an ignition device 27 is installed inside the combustion chamber. The steam generation chamber 28 surrounds the outside of the combustion chamber. The water in the steam generation chamber 28 is heated by the heat of hydrogen-oxygen mixed combustion, and under high temperature and high pressure conditions, it becomes high-pressure steam. Temperature sensors 17 (0 - 1000 °C) and pressure sensors 18 (0 - 30 MPa) are installed inside it to monitor the steam generation situation in real time.

[0050] A water injection pipeline 10 is led out from the ground gas injection station 12. The water injection pipeline 10 is divided into a hydrogen pipeline 19 and an oxygen pipeline 20. A water injection pipeline 9 is led out from the ground water injection station 15 and connected to the borehole steam furnace 5 of the injection hole 3. A flow meter is installed on the pipeline to control the stable water inflow at 12 m 3 / h.

[0051] A steam pipeline 29 is led out from the outlet of the borehole steam furnace 5. The pipeline is made of high-temperature resistant material (resistant to 1000 °C high temperature). A pressure control valve 25 is installed on the steam pipeline 29. The pipeline passes through the steam buffer chamber 24 and the sealing device 26, and the end is connected to the borehole screen pipe 6 to ensure that steam evenly enters the coal seam fracture network.

[0052] A Φ100 mm extraction pipeline 11 is led out from the extraction hole 4 and rises to the ground. Check valves 22, temperature-pressure-flow sensors (temperature 0 - 1000 °C, pressure 0 - 20 MPa, flow rate 0 - 400 Nm 3 / h), and a cyclone demister are installed on the pipeline to remove moisture and dust carried in the gas.

[0053] After the pipeline installation is completed, an airtightness test is carried out. Nitrogen is filled into the system to 18 MPa and the pressure is maintained for 36 hours. A pressure drop ≤ 0.3 MPa is qualified. At the same time, the linkage function of the central control system with sensors and valves is debugged to ensure that the parameter acquisition interval ≤ 1 s, the remote control response time of the valve ≤ 8 s, and the fault alarm accuracy rate is 100%.

[0054] Step S4, injection of reaction gas.

[0055] Hydrogen and oxygen are injected into the borehole steam furnace 5 through the injection pipeline 10. According to the combustion heat balance calculation, the set hydrogen injection volume is 65 Nm 3 / h, oxygen injection rate 32.5Nm 3 The gas mixture (volume ratio 2:1) burns two gases in the furnace at a rate of 850℃, while simultaneously injecting demineralized water through injection pipe 9. The water vaporizes at 850℃ and 4MPa, producing high-temperature, high-pressure steam. A "step-by-step pressurization" strategy is used to control the injection pressure: In the initial stage (0-24 hours), the steam pressure is set to 4MPa, and the gas production at extraction hole 4 is observed. Simultaneously, the pressure at extraction hole 4 is adjusted to 0.1MPa, maintaining a pressure difference of 3.9MPa. This pressure difference drives the steam to flow along the fracture network from injection hole 3 to extraction hole 4, ensuring full contact with the coal seam. The steam temperature, pressure, and extracted gas composition are monitored in real-time by a monitoring system: When the hydrogen concentration is below 30%, the steam temperature is increased to 900℃ (increasing by 50℃ each time, not exceeding the upper limit of 1000℃); when the injection pressure abnormally increases (exceeding 18MPa), it is determined that the coal seam fracture permeability has decreased, and the injection flow rate is reduced by 10% (not less than 50% of the rated flow rate) to ensure the continuous and stable gasification reaction.

[0056] Step S5: Product gas extraction.

[0057] The extraction method employs a combination of negative pressure suction as the primary method and positive pressure displacement as a secondary method. A vacuum pump (rated extraction capacity 400 Nm³) is installed at ground gas gathering station 13. 3 The vacuum pump, with a negative pressure range of 0-0.09 MPa, is connected to the extraction hole 4 via the extraction pipeline 11, generating a negative pressure of 0.07 MPa to extract the mixed gas (hydrogen, methane, tar, steam, etc.) from the coal seam to the surface gas gathering station 13. Simultaneously, the positive pressure of the 4 MPa injection pressure accelerates the gas convergence towards the extraction hole 4, improving extraction efficiency. During the extraction process, the extraction flow rate is stabilized at 350 Nm³ / h using the flow sensor 21. 3 When the pipeline pressure abnormally increases (exceeding 6 MPa) per hour, tar blockage is detected. The pipeline heating device (heating temperature 140℃) is activated to melt the tar and discharge it with the gas. When the gas humidity exceeds 20%, the demister is activated to reduce the gas moisture content to below 10% to avoid affecting subsequent separation processes. Gas samples are collected every 24 hours and analyzed using a gas chromatograph to ensure that separation and recovery conditions are met.

[0058] Step S6: Product separation and recovery.

[0059] A three-stage separation and recovery system is constructed on the ground, utilizing physical properties to achieve efficient separation. The first stage of tar separation employs a "gravity settling + filtration" process. The extracted gas is introduced into a 4m wide, 8m high gravity settling tank, where it remains for 25 minutes. The separation is achieved through density differences (tar density 1.08g / cm³). 3The gas density (0.09 kg / m³) causes 80% of the tar to settle. After further filtration through a Φ1000 mm sintered metal filter element (10 μm pore size), the tar content is reduced to 0.2 g / Nm³. 3 The tar is then collected and transported to 100m. 3 Storage tank. Secondary moisture removal: A dual-tower adsorption drying process is used. The drying tower is filled with 3A molecular sieves (adsorption capacity 25%). The gas stays in the tower for 15 seconds, during which the molecular sieves adsorb moisture, lowering the gas dew point to below 45℃. The dried gas then enters a 300m³ storage tank. 3 Buffer tank for pressure stabilization. Three-stage gas purification: A tower pressure swing adsorption (PSA) device is used, with activated carbon 5A molecular sieve composite packing as the adsorbent. The adsorption pressure is set at 2.5 MPa, the desorption pressure at 0.04 MPa, the adsorption time at 100 seconds, and the desorption time at 50 seconds. Impurities such as methane and carbon monoxide are selectively adsorbed by the adsorbent to purify hydrogen. A portion of the purified hydrogen is transported to the ground injection station 12 for recycling via hydrogen recovery pipeline 14, while the remainder is transported to surrounding areas via pipeline.

[0060] Step S7: Cooling of the waste slag deposit.

[0061] Ambient temperature desalination cooling water is injected into the gasified high-temperature coal seam waste slag deposit from the surface water injection station 15 via water injection pipeline 9. The extraction well 4 from the in-situ gasification stage is used as a pumping well. The original gas extraction pipeline is temporarily dismantled, and a water pump is installed inside the well to pump water and accelerate the flow of cooling water. Depending on the ore seam depth, the water injection operation can be stopped when the temperature of the pyrolytic coal seam waste slag drops to 95℃ after water injection and cooling. This provides conditions for subsequent leaching of valuable metals with water-based leaching solutions, while also providing a higher initial water temperature to enhance the efficiency of subsequent leaching chemical reactions.

[0062] Step S8: Inject the ground leaching solution.

[0063] After in-situ gasification, a coal seam waste deposit is formed, mainly composed of coke and semi-coke, at a depth of 580m. The waste residue has a porosity of 35%-45% and a permeability of 5-8mD. Testing revealed that the waste residue contains aluminum, iron, and trace amounts of gallium, making it suitable for in-situ leaching. Based on the types and forms of metals in the waste residue, a mixed acidic leaching solution of sulfuric acid and fluorosilicic acid was selected for aluminum and iron (a hydrochloric acid-sodium chloride system was used as an auxiliary leaching solution for gallium). Injection hole 3 from the in-situ gasification stage was used as the injection well, with a borehole diameter of 0.15m and an end screen to ensure uniform penetration of the leaching solution. An acid-resistant plunger pump was used for injection, with an injection pressure set at 12MPa and a flow rate maintained at 50m³ / h. The pressure difference drove the leaching solution to diffuse along the fracture network of the waste residue. During injection, a pH sensor installed inside the borehole monitored the chemical properties of the leaching solution in real time. When the pH value rose above 2.0, concentrated sulfuric acid was automatically added to adjust the concentration. Seven days after injection, the concentration of leachate around the waste residue was analyzed by sampling from the extraction borehole. When the concentration of aluminum ions in the leachate reached 5 g / L, the concentration of iron ions reached 3 g / L, and the concentration of gallium ions reached 0.02 mg / L, it was determined that the leachate had fully reacted with the metal and the extraction stage began.

[0064] Step S9: Extract the leachate.

[0065] The leaching solution was extracted using a combination of negative pressure extraction and positive pressure displacement. Extraction well 4 from the in-situ vaporization stage was used as the extraction well, and a corrosion-resistant vacuum pump (negative pressure range 0-0.09 MPa, extraction rate 0-80 m³ / h) was installed on the surface. 3 The vacuum pump, connected to the extraction well 4 via the acid-resistant fiberglass extraction pipeline 11, generates a negative pressure of 0.08 MPa to pump the metal-containing leachate to the surface; simultaneously, it maintains a positive pressure of 12 MPa in the injection well, stabilizing the injection-extraction pressure difference at approximately 12 MPa, thus accelerating the convergence of the leachate towards the extraction well 4. An electromagnetic flowmeter (range 0-100 m) is installed on the extraction pipeline 11. 3 The system uses a pressure sensor ( / h) to monitor the extraction flow rate and pipeline pressure in real time. The extracted leachate first enters a gravity settling tank, where it remains for 7 days to remove suspended coal slag particles. Then, it is filtered by a plate and frame filter press to obtain a clear metal-containing leachate.

[0066]

Example 2

[0067] This implementation method, based on the object of Example 1, relies on the underground excavated roadway to carry out high-temperature steam in-situ coal leaching for hydrogen production and in-situ metal leaching of waste residue. The specific operation is as follows: Step S1, extraction drilling construction.

[0068] During the drilling phase, based on the coal seam geological exploration data, parallel boreholes, including injection holes 3 and extraction holes 4, are uniformly distributed along roadway 30 in the roof of the coal seam (roadway 8, section 30). Figure 5 and Figure 6 As shown in the figure, the distance between the injection holes 3 and the drainage holes 4 is 20 m. The ends of the boreholes extend to the core area of the target coal seam. After the construction is completed, borehole screens 6 are installed in the coal seam section, and the borehole walls are consolidated to prevent borehole collapse from affecting subsequent operations.

[0069] Step S2: Fracturing for enhanced permeability.

[0070] In the fracturing for enhanced permeability process, the pulse hydraulic fracturing technology is adopted. In the roadway 30, fracturing fluid is alternately injected into the injection holes 3 and the drainage holes 4 through a high-pressure water injection pump. The average water pressure is controlled at 20 MPa, and the pulse frequency is adjusted to 30 Hz. After the fracturing, the unidirectional water injection method is used to test the connectivity. If the water injection flow rate is stable above 10 m 3 / h, it is determined that the connectivity is qualified. If not up to the standard, continue fracturing until the requirements are met.

[0071] Step S3: Installation of steam in-situ leaching facilities.

[0072] Within 100 m from the borehole mouth in the roadway 30, one high-temperature steam boiler with a rated power of 1000 kW is installed. The outlet of the steam boiler is connected to a high-temperature-resistant gas injection pipeline 10. The pipeline material is selected as high-temperature-resistant alloy, and the pressure resistance level is not less than 30 MPa. One-way valves 22 and temperature-pressure-flow integrated sensors are installed on the gas injection pipeline 10 and the drainage pipeline 11 respectively, and the sensor data is transmitted to the central control system in the roadway 30 in real time. A packer 26 is provided outside the borehole screen 6 to form an effective seal at the bottom of the borehole. The other end of the drainage pipeline 11 extends to the separation device in the roadway 30 to form a complete gas circuit circulation system. After the pipeline installation is completed, an airtightness test is carried out. Nitrogen is filled into the system to 18 MPa and the pressure is maintained for 36 hours. If the pressure drop ≤ 0.3 MPa, it is qualified. At the same time, debug the linkage function of the central control system with the sensors and valves to ensure that the parameter acquisition interval ≤ 1 s, the remote control response time of the valves ≤ 8 s, and the fault alarm accuracy rate is 100%.

[0073] Step S4: Injection of reaction gas.

[0074] During the gas injection stage, start the steam boiler, control the outlet steam temperature at 700 °C, and adjust the pressure to 3 MPa. The high-temperature and high-pressure steam flows through the gas injection pipeline 10 to the end of the injection hole 3 and evenly enters the coal seam fracture network through the borehole screen 6. At the same time, set the drainage pressure of the drainage hole 4 to 0.1 MPa to keep the pumping-injection pressure difference at 2.9 MPa. Use the pressure difference to drive the steam to flow from the injection hole 3 to the drainage hole 4 in the fracture network and react with the coal body by pyrolysis gasification. During the reaction process, the temperature, pressure and flow changes in the pipeline are monitored in real time through sensors, and the operation parameters of the steam boiler are dynamically adjusted according to the data feedback.

[0075] Step S5: Extraction of product gas.

[0076] The extraction operation employs a combination of positive pressure displacement and negative pressure suction. Once the gasification reaction within the coal seam stabilizes, a negative pressure of 0.02 MPa is applied through the extraction pump at extraction hole 4, with the extraction flow rate controlled at 200 Nm³. 3 Approximately [amount] / h. During the extraction process, the gas composition is continuously monitored. When the hydrogen concentration is below 30%, the injection temperature is appropriately increased to ensure hydrogen production efficiency.

[0077] Step S6: Product separation and recovery.

[0078] In the separation and recovery process, a separation device is installed in the tunnel 30. First, the tar in the mixed gas is separated by gravity sedimentation. After the tar is collected, it is transported to the ground storage tank through a closed pipeline. Then, the pressure swing adsorption method is used to separate hydrogen from waste gases such as methane and carbon monoxide based on the difference in gas density. After the hydrogen purity is purified to 99.9%, it is stored in a high-pressure hydrogen storage tank or directly transported to the ground pipeline network. Some hydrogen and methane are used as auxiliary fuel for the steam furnace. The waste gas is discharged in compliance with standards after desulfurization and denitrification treatment.

[0079] Step S7: Cooling of the waste slag deposit.

[0080] Ambient temperature desalination cooling water is injected into the gasified high-temperature coal seam waste slag deposit from the surface water injection station 15 via water injection pipeline 9. The extraction well 4 from the in-situ gasification stage is used as a pumping well. The original gas extraction pipeline is temporarily dismantled, and a water pump is installed inside the well to pump water and accelerate the flow of cooling water. Depending on the ore seam depth, the water injection operation can be stopped when the temperature of the pyrolytic coal seam waste slag drops to 95℃ after water injection and cooling. This provides conditions for subsequent leaching of valuable metals with water-based leaching solutions, while also providing a higher initial water temperature to enhance the efficiency of subsequent leaching chemical reactions.

[0081] Step S8: Inject the ground leaching solution.

[0082] After in-situ gasification of the coal seam, a coal seam waste deposit is formed, mainly composed of coke and semi-coke. The waste contains aluminum, iron, and trace amounts of gallium, making it valuable for in-situ leaching. Based on the types and forms of metals in the waste, sodium hydroxide alkaline leaching solution can be used for aluminum and gallium. Injection hole 3 from the in-situ gasification stage is used as the injection well, with a screen at the end ensuring uniform penetration of the leaching solution. Two alkali-resistant plunger pumps are used, with the injection pressure set at 8 MPa, utilizing the pressure difference to drive the leaching solution to diffuse along the fracture network of the waste. During injection, a pH sensor installed in the borehole monitors the chemical properties of the leaching solution in real time. When the pH value drops above 13.0, sodium hydroxide is automatically added to adjust the concentration. Seven days after injection, samples are taken from the extraction borehole to analyze the concentration of the leaching solution around the waste. When the aluminum ion concentration in the leaching solution reaches 5 g / L and the gallium ion concentration reaches 0.02 mg / L, it is determined that the leaching solution has fully reacted with the metals, and the extraction stage begins.

[0083] Step S9: Extract the leachate.

[0084] The leaching solution was extracted using a combination of negative pressure extraction and positive pressure displacement. Extraction well 4 from the in-situ gasification stage was used as the extraction well, and a corrosion-resistant vacuum pump (negative pressure range 0-0.09 MPa, extraction capacity 0-80 m³) was installed within roadway 30. 3 The vacuum pump, connected to the extraction well 4 via the corrosion-resistant fiberglass extraction pipeline 11, generates a negative pressure of 0.08 MPa to pump the metal-containing leachate to the surface; simultaneously, it maintains a positive pressure of 8 MPa in the injection well, stabilizing the injection-extraction pressure difference at approximately 8 MPa, thus accelerating the convergence of the leachate towards the extraction well 4. An electromagnetic flowmeter (range 0-100 m) is installed on the extraction pipeline 11. 3 The system uses a pressure sensor ( / h) to monitor the extraction flow rate and pipeline pressure in real time. The extracted leachate is transported to the ground and enters a gravity settling tank, where it remains for 7 days to remove suspended coal slag particles. Then, it is filtered by a plate and frame filter press to obtain a clear metal-containing leachate.

[0085] This high-temperature steam in-situ leaching method for producing hydrogen from coal and its waste residue for in-situ leaching of metals no longer involves directly injecting oxygen into the coal seam or directly igniting the coal seam. Instead, it injects high-temperature steam into the coal seam, which reacts with carbon in the coal seam through pyrolysis and gasification, thereby achieving underground pyrolysis and gasification of the coal and producing combustible gases such as hydrogen. Then, the metal resources in the waste residue deposit after gasification are developed and utilized using the principle of in-situ leaching.

[0086] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these should also be considered within the scope of protection of the present invention. These will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A method for producing hydrogen from coal by high-temperature steam leaching and for extracting metals from waste residue by leaching, characterized in that, Includes the following steps: S1. Drainage drilling construction: Drill at least two parallel boreholes into the same coal seam on the surface or in the underground roadway. Install screen pipes in the boreholes, which serve as steam injection holes and hydrogen extraction holes, respectively. S2. Fracturing and Permeability Enhancement: Fracturing the coal seam using injection holes and extraction holes to form a network of interconnected fractures between the boreholes; S3. Steam leaching facility installation: A steam generator is installed, and its outlet is connected to the coal seam fracture network through a steam pipeline and a borehole screen. An extraction pipeline is installed in the extraction hole to lead to the surface. S4. Reaction gas injection: Reaction gas is introduced into the steam generator and / or electrical energy is used to directly or indirectly generate high-temperature and high-pressure steam, which is discharged into the steam pipeline and flows into the coal seam fracture network through the perforated screen at the end of the steam pipeline. S5. Product gas extraction: High-temperature steam is made to flow from the injection hole to the extraction hole along the fracture network using the injection pressure difference. It reacts with the coal through pyrolysis and gasification, and the generated products such as hydrogen are extracted to the ground through the extraction hole. S6. Product Separation and Recovery: Separate and recover hydrogen from the extracted product; S7. Cooling of waste slag deposit: Cooling water is injected into the coal seam waste slag deposit formed after gasification to reduce the temperature of the coal seam after pyrolysis. S8. Injection of leaching solution: Injecting leaching solution into the cooled waste slag deposit to dissolve the valuable metals therein and form a leaching solution; S9. Extraction of leaching solution: Extracting the leaching solution from the waste slag deposit for metal recovery.

2. The method for producing hydrogen from coal by high-temperature steam leaching and mining metals from waste residue according to claim 1, characterized in that, In step S1, when drilling in the roadway, the drilling direction is perpendicular to the roadway wall; when drilling on the ground, the drilling direction is vertically downward; the drilling depth is equal to the local average burial depth of the target coal seam and does not penetrate the coal seam floor; the distance between the boreholes is not less than 10 meters.

3. The method for producing hydrogen from coal by high-temperature steam leaching and mining metals from waste residue according to claim 1, characterized in that, In step S2, the fracturing and permeability enhancement method is pulsed hydraulic fracturing; during fracturing, the fracture distribution is assessed by microseismic monitoring, and after fracturing, the connectivity of the fracture network between boreholes is assessed by unidirectional water injection.

4. The method for producing hydrogen from coal by high-temperature steam leaching and mining metals from waste residue according to claim 1, characterized in that, In step S3, the steam generating device is a surface steam boiler, an underground roadway steam boiler, or a borehole-type steam boiler installed in a borehole; when the steam boiler is located on the surface or in a roadway, the steam pipeline is insulated; when a borehole-type steam boiler is used, it is located above the coal seam and within 0-50 meters of the gasified coal seam; the pipeline system is equipped with flow, temperature, and pressure sensors, as well as check valves and flame-retardant valves.

5. The method for producing hydrogen from coal by high-temperature steam leaching and mining metals from waste residue according to claim 1, characterized in that, In step S4, the method for generating high-temperature and high-pressure steam is as follows: hydrogen and oxygen are injected into the steam generator, and they are mixed and burned to generate high temperature, while the injected water is heated to generate high-temperature and high-pressure steam; or, the injected water is heated by electric energy to generate high-temperature and high-pressure steam; the temperature of the high-temperature and high-pressure steam is 300-1000℃, and the pressure is controlled according to the coal seam conditions and the gas injection volume requirements.

6. The method for producing hydrogen from coal by high-temperature steam leaching and mining metals from waste residue according to claim 1, characterized in that, In step S5, the injection-extraction pressure difference is achieved by controlling the positive pressure of the injection hole steam and / or the negative pressure of the extraction hole, using positive pressure displacement, negative pressure suction, or a combination of both.

7. The method for producing hydrogen from coal by high-temperature steam leaching and mining metals from waste residue according to claim 1, characterized in that, In step S6, the separation and recovery includes: separating tar by gravity sedimentation and filtration, removing moisture by adsorption drying, and purifying hydrogen by pressure swing adsorption.

8. The method for producing hydrogen from coal by high-temperature steam leaching and mining metals from waste residue according to claim 1, characterized in that, In step S7, the cooling water is desalinated ambient temperature cooling water, and the final cooling temperature keeps the water in a liquid state under the pressure environment of the coal seam waste ore deposit.

9. The method for producing hydrogen from coal by high-temperature steam leaching and mining metals from waste residue according to claim 1, characterized in that, In step S8, the coal seam waste ore deposit is coke and semi-coke with a porous structure; the leaching solution is selected according to the type of target metal in the waste ore, including acidic or alkaline leaching solution systems.

10. The method for producing hydrogen from coal by high-temperature steam leaching and mining metals from waste residue according to claim 1, characterized in that, In step S9, the extraction of the leachate is carried out by a combination of negative pressure extraction and positive pressure displacement, using existing gasification stage extraction wells or newly established extraction wells.

Images