A closed-loop filling process and system for in-situ gasification pipe extraction of metal in coal gangue goaf.

Abstract

This invention discloses a closed-loop filling process and system for in-situ gasification of coal gangue in goaf areas, involving metal extraction through pipes. After pretreatment, open-pit coal gangue is pneumatically fed into the underground goaf area and mixed with in-situ carbonaceous shale to form a gasification bed. Gasification is performed using atmospheric pressure air, with the raw material self-heating to maintain a gasification temperature of 890–1040°C. High-temperature flue gas is directly transported to a flue gas turbine for power generation, eliminating the need for intermediate heat exchange equipment. The crude syngas is refined and then subjected to horizontal catalytic cracking to produce oil, achieving cascade cogeneration of heat and power and oil products. Gasification ash is collected under negative pressure underground and undergoes a four-stage closed-loop separation process: through electromagnetic separation, cyclone separation, electrostatic separation, and X-ray separation, seven metal concentrates (iron, aluminum, vanadium, gallium, copper, nickel, and chromium) are separated. The concentrates are pressurized and sent to surface storage in a closed system. The tailings are then pneumatically filled into the goaf area using residual pressure, with zero tailings being stockpiled underground. This invention reduces equipment investment, minimizes heat loss and waste residue, improves energy consumption, overcomes the drawbacks of magnetic separation clogging, and integrates solid waste disposal, multi-metal recovery, mining subsidence remediation, power generation and oil production, with outstanding energy-saving and environmental protection advantages.

Description

Technical Field

[0001] This invention belongs to the field of green mining resource utilization technology, including underground in-situ air gasification of coal gangue, high-temperature flue gas direct-drive flue gas turbine power generation, low-temperature horizontal flow catalytic oil production, underground closed pipeline dry multi-metal separation, valuable concentrate diversion and lifting to the surface, and underground closed-loop backfilling of tailings. Background Technology

[0002] Existing similar processes have several shortcomings in the industry: 1. Traditional in-situ gasification systems, combined with air separation for oxygen enrichment and boiler steam generation, involve large equipment investments and high energy consumption for system operation and maintenance. 2. Conventional gasification of high-temperature flue gas generally uses heat exchangers to generate steam and then generate electricity. Multi-stage heat exchange results in significant heat loss due to temperature differences, low thermal energy utilization, and additional infrastructure and maintenance costs for heat exchangers and thermal oil equipment. 3. All gasification ash and slag are lifted to the ground for sorting and separation. The long-distance lifting of bulk tailings to the well results in serious energy waste. The supporting open-air tailings storage yard is prone to environmental hazards such as dust and heavy metal leaching. 4. Traditional tubular magnetic separators use permanent magnet structures, and iron-containing minerals continuously adhere to the inner wall of the magnet, making automatic unloading impossible. The machine must be stopped, the tube broken, and the material manually cleaned, making continuous and stable production impossible. 5. Valuable concentrate and tailings are transported through the same pipeline, which makes it impossible to extract concentrate separately and backfill tailings on-site, resulting in an unreasonable allocation of resources and energy. 6. Most processes rely solely on syngas for power generation, resulting in low product added value and poor resource utilization.

[0003] The existing technology lacks an integrated process for atmospheric pressure air self-sustaining gasification, high temperature flue gas direct entry into flue gas turbine for power generation without heat exchange, syngas co-production of oil products, full-component ash and slag underground on-site separation, valuable ore small pipeline branching to the well, and inert tailings underground closed-loop backfilling, which is the existing technology gap that this invention aims to fill. Summary of the Invention

[0004] The technical problem that the invention aims to solve: 1. Abandoning the complete set of equipment for oxygen-enriched preparation and external steam boilers, relying solely on atmospheric pressure air to achieve self-sustaining high-temperature gasification of raw materials, thereby reducing the initial equipment investment and annual operating energy consumption of the project; 2. Eliminate intermediate heat exchange facilities for flue gas, and directly feed high-temperature raw flue gas into the flue gas turbine for expansion and power generation, thereby eliminating heat loss in the heat exchange process, improving heat conversion efficiency, and reducing the purchase cost of heat exchange equipment; 3. All sorting units are centrally located underground. Large quantities of inert tailings are backfilled nearby underground and no longer need to be brought to the surface. Only the valuable enriched concentrate is pressurized to the surface through small-flow branch pipelines, completely eliminating the ineffective energy consumption caused by the full-area slag shoveling. 4. The tubular magnetic separator adopts an external ring electromagnetic excitation structure, which attracts iron ore when the magnet is turned on and automatically unloads the material when the power is cut off intermittently. Combined with the closed screw for continuous discharge, it solves the industry pain points of permanent magnet sticking to the wall and clogging the pipe and stopping the machine to clean the material from the root. 5. After purification, the syngas is further processed into Fischer-Tropsch oil, forming a dual-product co-production of power generation and oil products, thereby increasing the added value of comprehensive resource utilization; 6. Gangue is fed into the mine in the forward direction, and inert tailings are used to fill vacant underground goaf areas nearby, thus reducing investment in pipeline construction.

[0005] The overall technical solution comprises seven major units: 1) Surface raw material pretreatment + gangue conveying unit: After screening and grading, the coal gangue stored in the open pit is crushed at a single point using a mobile crusher if the particle size is >50mm. The raw powdery gangue is directly and sealed in the ground storage silo. The ground is equipped with a silo-type pneumatic conveying pump with a conveying pressure controlled at 0.3-0.38MPa. Through a single sealed main conveying pipeline, the coal gangue is continuously sent to the independent sealed gasification chambers of each section underground under positive pressure. The gangue is spread flat on the surface of the original carbonaceous shale in the chamber. The carbonaceous shale is retained in situ and is not mined or removed from the mine.

[0006] 2) Downhole atmospheric pressure air self-sustaining gasification + flue gas direct expansion power generation + syngas to oil cogeneration unit: Each gasification zone is supplied with ambient temperature and pressure air through ground low-pressure air supply pipelines as the sole gasification medium. It relies on the self-sustaining oxidation and heat release of gangue and carbonaceous shale organic matter. The cavity is stably maintained at a gasification temperature of 890-1040℃. There is no air separation oxygen production or external steam supply. High-temperature flue gas is purified and then directly used for power generation: The cavity produces high-temperature raw flue gas of 520-650℃, which is directly led to the ground flue gas turbine through a high-temperature alloy sealed pipeline. The adiabatic expansion of the high-temperature flue gas drives the generator set to generate electricity directly. There are no pre-embedded heat exchange tube bundles in the cavity or heat transfer equipment for heat transfer oil / hot water, eliminating heat exchange heat loss. After the flue gas turbine does its work, the low-temperature exhaust gas is led back to the plant area to dry auxiliary raw materials, and the waste heat is utilized in a cascade manner without waste. Syngas deep processing into oil: The crude syngas from each chamber in the well is collected, purified by dust removal and power generation, and then sent to a horizontal catalytic reactor to catalyze the production of light fuel oil and naphtha products. A small amount of by-product tail gas is added to the system to assist in temperature regulation.

[0007] 3) Downhole negative pressure slag removal and conveying unit: After the single-zone gasification process is completed, the underground negative pressure induced draft fan is started to form a negative pressure suction environment in the ash and slag conveying main pipe. All powdered activated ash and slag inside the cavity are conveyed in a closed manner along the main pipe. The ash and slag do not fall to the ground or rise to the surface throughout the process, and are directly sent to the four-stage series sorting assembly installed in the underground roadway.

[0008] 4) Downhole segmented speed-regulating four-stage tubular online sorting unit: The airflow velocity of the ash conveying main pipe is controlled in sections: magnetic separation section 9-13m / s, cyclone section 14-17m / s, electrostatic section 16-19m / s, X-ray separation section 12-15m / s; ① First-stage annular electromagnetic separation module: The outer wall of the conveying pipeline is surrounded by an annular excitation electromagnetic coil. When energized, a high-strength magnetic field of 8000-1200Gs is formed on the pipe wall, and iron minerals in the airflow are adsorbed onto the inner wall of the pipeline. The control system intermittently cuts off the power and demagnetizes according to a fixed sequence. The magnetic field on the pipe wall disappears instantaneously, and the iron concentrate automatically falls off into the side collection chamber by its own weight and the flushing of the pipeline airflow. A closed screw conveyor is matched on the side of the module to continuously feed the material outward. ② Secondary cyclone gravity separation module: Based on the difference in mineral density, it separates and enriches valuable components such as aluminum and vanadium from heavy ash slag; ③ Three-stage tubular electrostatic separation module: Utilizing the natural triboelectric charge difference of high-temperature ash slag, aluminum-based enriched materials are purified in a secondary manner; ④ The four-stage pipeline is embedded with an X-ray intelligent sorting module: X-rays are used to identify fine gallium, copper, nickel and chromium individual particles online, and the rare metals are enriched and separated by fixed-point pulsed airflow.

[0009] 5) Polymetallic enriched mine underground booster and lifting unit: Each of the four-stage sorting modules is equipped with an independent bypass closed discharge structure: iron concentrate is fed through a spiral discharge mechanism, while aluminum, vanadium, gallium, copper, nickel, and chromium sorting products adopt an upper and lower double-plate air-locking bypass structure, relying on the staggered opening and closing of dual valves to intermittently and closedly collect materials under the condition of uninterrupted main airflow; each discharge branch is equipped with a small underground special booster pump, which is connected to an independent small-diameter closed branch pipeline, and various valuable enriched ores are pressurized by a small flow rate and then transported to the corresponding closed finished product storage tank on the ground.

[0010] 6) Inert tailings underground near-closed-loop backfilling unit: The remaining inert tailings after the four-stage sorting rely on the residual air pressure of the pipeline to be connected to the feed side of the main pipeline through the underground closed diversion branch pipe. The reverse positive pressure air of the main pipeline is reused to continuously send it into other empty mined cavities in the mining area for compaction and filling. The tailings are disposed of underground on-site throughout the entire process, without any tailings being raised to the surface, without any open-air temporary storage yards, and without any waste residue pollution.

[0011] 7) Resource-based product storage and transportation unit: The generator sets produce electricity for the plant's own use, and surplus electricity is sold to the grid; the oil produced by the horizontal flow catalytic converter is stored in sealed storage tanks and then transported out for sale; various metal concentrates are stored in sealed warehouses and sent to refineries for further processing.

[0012] S1: Ground coal gangue screening and grading, large-piece crushing, and closed storage of powder materials; S2: The surface pump delivers the gangue under positive pressure in the dense phase, and the gangue enters the underground goaf section along the main pipeline to form a composite gasification bed with the in-situ carbonaceous shale; S3: Atmospheric pressure air enters the cavity and undergoes self-sustaining high-temperature gasification. The high-temperature flue gas is directly sent to the ground for purification, and then the flue gas turbine expands to generate electricity. The syngas is refined on the ground. S4: Most of the refined syngas is sent to a horizontal catalytic converter to produce fuel oil, and a small amount of tail gas is recycled by the system. S5: Single-chamber gasification ends, downhole negative pressure unit sucks up all activated ash and slag, and the ash and slag enter the four-stage sorting system through the entire downhole pipeline. S6: The electromagnetic separation module is intermittently powered on and off to achieve automatic unloading of iron concentrate, while other valuable minerals are intermittently discharged through a double-valve air-lock bypass. S7: Various enriched concentrates are pressurized through small underground booster pumps and transported to surface storage tanks via independent closed branch pipes; S8: After sorting, the inert tailings are connected to the main pipeline nearby, and the idle goaf is filled with uninterrupted reverse pneumatic filling, with zero tailings being lifted to the well throughout the entire process. Beneficial effects

[0013] 1. Eliminate all supporting facilities for intermediate heat exchange of flue gas, and use high-temperature flue gas to directly drive the flue gas turbine to generate electricity, avoiding heat loss from multi-stage heat exchange, improving the system's thermal energy utilization rate by 18% to 22%, saving approximately RMB 3.8 million in investment in heat exchangers and thermal oil furnaces, and simultaneously reducing the annual operation and maintenance costs of heat exchange equipment. 2. Eliminating the entire air separation oxygen production and steam boiler system reduces the project's initial construction investment by more than 30%, and eliminates the year-round water, electricity, and coal consumption for air separation and steam production; 3. All sorting equipment is centrally deployed underground. Large quantities of inert tailings, accounting for about 57% of the total raw materials, are backfilled on-site underground and cannot be brought to the surface. Energy consumption for lifting waste residue to the surface is reduced by more than 35%. Large-scale surface tailings storage yards are eliminated, and environmental risks such as tailings dust and rainwater leaching of heavy metals are eliminated. 4. The tubular annular electromagnetic intermittent excitation unloading structure attracts iron when energized and automatically discharges material when demagnetized. It is equipped with a closed spiral for continuous material discharge, which completely solves the drawbacks of permanent magnet sorting, such as sticking to the wall and clogging the pipe, and manual cleaning during shutdown, and ensures long-term continuous and stable production of the system. 5. Only small-volume concentrates are raised to the surface using narrow-diameter branch pipelines, equipped with small underground booster pumps. Compared with the full slag raising scheme, the power of the conveying equipment is greatly reduced and the energy consumption of conveying is significantly optimized. 6. Gangue is fed directly into the mine and tailings are backfilled, eliminating the need for a separate long-distance pipeline network for backfilling, thus reducing the investment in pipeline construction and materials; 7. Syngas is refined and then catalytically converted into oil, forming a diversified product structure of power generation + oil products + polymetallic concentrates, breaking through the limitations of single power generation revenue and significantly increasing the comprehensive added value of solid waste resource utilization; 8. The entire system operates in a closed pneumatic circulation mode, with no dust or solid waste discharge, which is in line with the five major economic and environmental benefits of mine ecological restoration, comprehensive utilization of bulk solid waste, solid waste disposal, multi-metal recovery, mining subsidence treatment, power generation, and oil production. Attached Figure Description

[0014] Figure 1: Overall Process Diagram of the Co-production System Attached reference numerals: 1 - Surface raw material pretreatment unit; 2 - Surface silo pump into well conveying unit; 3 - Downhole gasification unit; 4 - Negative pressure slag removal unit; 5 - Sorting unit; 6 - Concentrate lifting unit; 7 - Tailings backfilling unit; 8 - Cogeneration unit for thermal energy and syngas resources; 9 - Sealed main pipeline; 10 - Goaf cavity; 11 - Sealed surface storage silo; 12 - High-temperature resistant sealed pipeline; 13 - Negative pressure pipeline; 14 - Sealed branch pipeline. Detailed Implementation Example

[0015] The closed and abandoned coal mine is divided into 4 independent underground gasification chambers, each with an effective volume of 60,000 to 120,000 m³. The carbonaceous shale interlayers in the underground coal seam are left in situ and not mined. The project will accept and process 820,000 tons of open-pit coal gangue annually. 77% of the raw materials have a particle size of ≤30mm, and oversized lumps will be crushed as needed.

[0016] 1. The surface silo pump uses a 0.35MPa dense phase feeding system, with a coal gangue and in-situ carbonaceous shale feed ratio of 6.5:3.5. At ambient temperature and pressure, air is introduced into the underground working chamber for self-sustaining gasification, with a stable operating temperature of 910–970℃. The high-temperature flue gas from the chamber is directly transported to the surface flue gas turbine for power generation via a high-temperature resistant pipeline, eliminating all heat exchange equipment. Compared to the heat exchange-based steam generation power generation scheme, this method increases annual power generation by 19.5% with the same raw material consumption. 2. Simultaneously, the crude syngas is purified by a purifier and then used to generate electricity through a flue gas turbine. 62% of the refined syngas is sent to a horizontal catalytic converter to produce light fuel oil, and the remaining syngas tail gas is reused internally for temperature regulation. 3. After single-chamber gasification is completed, the underground negative pressure fan pumps all the powdery ash and slag into the underground segmented speed-regulating four-stage separation; the electromagnetic coil is set to de-energize and discharge material every 15 minutes, and the iron concentrate is continuously discharged through a closed screw conveyor; the actual separation indicators are: Fe roughing recovery rate 60.2%, Al component enrichment 4.8 times, V2O5 enrichment 4.35 times, Ga enrichment 8.9 times, Cu enrichment 7.6 times, Ni enrichment 7.2 times, Cr enrichment 6.8 times; 4. The four types of valuable enriched products are pressurized by independent underground small-scale pumps and transported to sealed surface storage tanks through dedicated fine pipelines. The average daily total output of various concentrates is 21.3t. After sorting, inert tailings account for 57% of the gangue fed into the furnace. All of them are connected to the main pipeline through sealed branch pipes and continuously backfill the idle mined-out cavities. The tailings are lifted to the well and there is no surface stockpiling throughout the entire process.

[0017] Comparative example (traditional oxygen-enriched + boiler heat exchange + all-slag ground-based mineral processing): For the same annual processing capacity of 820,000 tons of gangue, the fixed equipment investment is more than 27 million yuan higher, including an air separation oxygen production station, steam boiler, large heat exchange system, ground ore dressing plant, and a 30,000 square meter tailings storage yard. The annual energy consumption for air separation steam production, electricity consumption for waste residue lifting to the well, and environmental protection operation and maintenance costs for tailings total more than 2.6 million yuan. The heat loss of flue gas heat exchange power generation is large and the power generation is low. Syngas only generates electricity without oil co-production, resulting in a single product structure and low overall returns.

Claims

1. A closed-loop filling process and system for in-situ gasification of coal gangue goaf with metal extraction in the pipeline, comprising a surface raw material pretreatment unit (1), a surface silo pumping unit (2), an underground gasification unit (3), a negative pressure slag removal unit (4), an underground sorting unit (5), a concentrate lifting unit (6), a tailings filling unit (7), and a thermal energy and syngas resource co-production unit (8); the surface raw material pretreatment unit (1) is connected to the surface silo pumping unit (2), the surface silo pumping unit (2) is connected to the gasification unit (3) in the underground goaf cavity (10) via a closed main pipeline (9), and the goaf cavity (10) is connected to each underground unit via a negative pressure pipeline (13); characterized in that: ① The underground gasification unit (3) only introduces ambient temperature and pressure air as the gasification medium. There is no oxygen enrichment preparation or external steam supply equipment. It relies on the self-sustaining heat release of the raw materials to maintain a gasification temperature of 890-1040℃. The high-temperature crude synthesis flue gas produced by gasification does not pass through intermediate heat exchange tube bundles or heat transfer oil / boiler heat exchange transfer. It is directly led out to the ground through a high-temperature resistant closed pipeline (12) and connected to the heat energy and synthesis gas resource co-production unit (8). After purification, it is expanded by the flue gas turbine to generate electricity. The synthesis gas is catalyzed by a horizontal flow catalytic device to produce oil products. ② The entire four-stage dry sorting unit (5) is arranged inside the underground goaf cavity (10) roadway. The gasified ash is transported and sorted throughout the entire process by the underground negative pressure pipeline (13). The inert tailings are no longer lifted to the surface, and the valuable minerals and tailings are disposed of separately. ③ The first section of the sorting is an electromagnetic separation module with an annular electromagnetic coil surrounding the outer wall of the pipeline. When energized, it adsorbs iron minerals and when the power is cut off intermittently, it loses magnetism to achieve automatic detachment of iron concentrate. The module is equipped with a closed spiral discharge mechanism on the side. ④ The sorting products at each level are connected to the small booster pump and the dedicated closed branch pipeline (14) in the mine. Various valuable enriched ores are transported to the surface closed storage silo (11) through the closed branch pipeline (14) with a small flow rate and pressure. The sorted inert tailings are continuously filled into the empty mining cavity in the mine through the closed diversion branch pipe.

2. The system according to claim 1, characterized in that: The working pressure of the ground-mounted pneumatic conveying pump is 0.3 to 0.38 MPa. Coal gangue is fed into the mine in the forward direction, and inert tailings are used to fill the empty underground goaf cavities nearby.

3. The system according to claim 1, characterized in that: The sorting unit features segmented speed regulation: airflow speeds of 9–13 m / s in the magnetic separation zone, 14–17 m / s in the cyclone zone, 16–19 m / s in the electrostatic zone, and 12–15 m / s in the X-ray separation zone. The sorting modules sequentially consist of tubular electromagnetic separation, cyclone gravity separation, tubular electrostatic separation, and X-ray online separation, separating seven valuable components—iron, aluminum, vanadium, gallium, copper, nickel, and chromium—in stages.

4. The system according to claim 1, characterized in that: The mass ratio of coal gangue and in-situ carbonaceous shale fed into the goaf (10) is controlled at 6:4 to 7:

3.

5. The system according to claim 1, characterized in that: The aluminum-vanadium and gallium-copper-nickel-chromium sorting bypass is equipped with an upper and lower double-plate air-locking discharge assembly, which relies on the staggered opening and closing of the dual valves to achieve intermittent closed discharge under the condition of continuous air supply in the main pipe; the discharge branch pipe of each sorting chamber is equipped with a timed high-pressure purging anti-clogging structure, and the inner wall of the sorting chamber is sprayed with a wear-resistant ceramic protective layer.

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