Underground gasification mining method and underground gasification furnace system for deep and super-thick coal seam

Abstract

The application discloses a kind of deep ultra-thick coal seam underground gasification mining method and underground gasification furnace system, belong to coal mining technical field, method includes the following steps: constructing multiple gasification furnaces in coal seam, each gasification furnace includes multiple vertical shafts, at least one of multiple vertical shafts is injection hole, the rest is as gas outlet hole;Gasification agent carrying filling material is injected into the injection hole of gasification furnace, so that coal seam occurs gasification reaction and the formed combustion empty area is filled synchronously;The filling material in the combustion empty area of completion gasification filling is maintained, so that it is consolidated into the whole with support strength, to form artificial isolated support zone;During gasification reaction, according to the volume change of different positions of combustion empty area, the function of injection hole and gas outlet hole in single gasification furnace is adjusted, so that the top form of combustion empty area is evenly expanded in the height direction of coal seam.The present application realizes nearly full mining of ultra-thick coal seam, and the stability of stratum structure is ensured by the high-strength support system constructed in situ.

Description

Technical Field

[0001] This invention belongs to the field of coal mining technology, and particularly relates to an underground gasification mining method and underground gasification furnace system for deep, ultra-thick coal seams. Background Technology

[0002] Underground coal gasification technology involves injecting a gasifying agent into underground coal seams through boreholes, causing the coal to pyrolyze, burn, and gasify into combustible gas, which is then collected and utilized on the surface. Due to its significant social and economic benefits, it is hailed as a new generation of coal mining technology and has broad application prospects in the mining and utilization of low-quality (high sulfur, high ash), steeply inclined, thin, deep coal seams, coal seams under pressure from underground elements, and other coal seams where conventional mining techniques are economically ineffective. While numerous industrial trials and commercialization efforts have been conducted both domestically and internationally, stable industrial production has yet to be achieved. One major reason is the relatively small scale of underground coal gasification. A key factor limiting large-scale underground coal seam gasification is the influence of high temperatures, gases, thermal fracturing of the coal body, surrounding rock stress, overburden caving, and fracture zone development within the underground gasification space. The underground goaf cannot be too large; otherwise, it will cause overlying strata subsidence, making the underground gasifier difficult to control. Alternatively, to avoid overlying strata subsidence, large coal pillars may be reserved, resulting in a low coal seam extraction rate.

[0003] Chinese patent application CN201910418349X discloses a method for underground gasification of extremely thick coal seams. The method involves constructing a horizontal well above the bottom of the coal seam, and a row of vertical wells above the horizontal well, connecting the horizontal and vertical wells. Packers are installed in the horizontal wells and gasifying agents are injected to gasify the coal seam. By setting packers to prevent the injection of gasifying agents in a certain section of the horizontal well, a portion of the coal seam is retained from gasification. The resulting reserved coal pillars support the overlying strata of the combustion zone, preventing large-scale collapse and enabling underground gasification mining of deep, ultra-thick coal seams. However, the need to reserve coal pillars results in a low mining rate for the underground coal seam.

[0004] Chinese patent application CN2018107969175 discloses an underground coal gasification channel and gasification method composed of a multi-layered U-shaped docking well group. The gasification channel includes vertically arranged exhaust wells with their lower ends extending into the coal seam, and multiple vertical injection wells arranged around the exhaust wells. The lower ends of the injection wells extend into the coal seam and are equipped with multiple branch wells facing and connected to the exhaust wells. During gasification, the branch wells in the same layer as each injection well are used as the gasification channel from top to bottom, and the exhaust wells are used as gas outlet wells to gradually gasify the coal seam, thereby achieving underground gasification of ultra-thick coal seams. However, top-down gasification can lead to large-scale collapse of the overlying rock strata due to loss of support, making the gasifier difficult to control or even causing blockage and shutdown.

[0005] Chinese patent application CN2025116231004 discloses a method for underground coal gasification and backfilling. The method includes: after gasification begins, determining a predetermined signal for backfilling based on the total effective component volume content of the gas from the vents, the output per unit time, or the expected cavity volume of the combustion chamber; injecting backfilling slurry into the combustion chamber through the gasifying agent injection hole, instantly or gradually switching the gasification mode to backfilling mode to maintain gas production from the vents; determining whether the expected backfilling target has been achieved by real-time monitoring of the temperature, effective component content, or gas production rate of the gas produced from the vents, or by real-time monitoring of whether the maximum backfilling volume for a single backfill has been reached; after achieving the expected backfilling target, instantly or gradually switching the backfilling mode to gasification mode; repeating the above steps until the gasified coal seam is fully mined. Wet backfilling and intermittent gasification / backfilling operations increase the difficulty of controlling the gasifier, and more importantly, the heat loss during gasification operation is significant, resulting in low gas production efficiency of the gasifier.

[0006] In summary, existing technologies for underground gasification of deep, ultra-thick coal seams either have technical problems such as large-scale collapse of the overlying strata in the combustion zone leading to ground subsidence, or they have problems such as the inability to mine coal seams on a large scale (requiring the reservation of coal pillars), resulting in a low coal seam mining rate, or the difficulty in controlling gasification operation and the low utilization efficiency of thermal energy in the gasifier due to backfilling. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a method for underground gasification mining of deep, ultra-thick coal seams and an underground gasifier system. This method enables near-full mining of ultra-thick coal seams while ensuring the stability of the geological structure through an in-situ constructed high-strength support system. This provides an efficient and safe technical path for the large-scale and industrialized underground gasification mining of deep coal resources.

[0008] This invention is implemented by providing a method for underground gasification mining of deep, ultra-thick coal seams, comprising the following steps:

[0009] Multiple gasifiers are constructed in the coal seam. Each gasifier includes multiple vertical shafts and a channel that runs through the bottom of each vertical shaft. At least one of the multiple vertical shafts is an injection hole, and the rest are gas outlet holes for collecting the produced coal gas.

[0010] A gasifying agent carrying filling material is injected into the injection hole of the gasifier to cause the coal seam to undergo a gasification reaction and to simultaneously fill the resulting combustion air zone.

[0011] The filling material in the gasification and filling zone is cured to solidify it into a whole with supporting strength, so as to form an artificial isolation support zone.

[0012] In the gasification process, the functions of the injection holes and exhaust holes in a single gasifier are adjusted according to the volume changes at different locations in the combustion zone, so that the top morphology of the combustion zone expands uniformly in the direction of coal seam height.

[0013] Furthermore, based on the volume changes at different locations in the combustion zone, the functions of the injection holes and outlet holes in a single gasifier are adjusted. Specifically, when the volume of the combustion zone formed at the injection location is greater than the volume of the combustion zone formed at the outlet location, the functions of the injection holes and outlet holes in the gasifier are adjusted; and the adjustment operation is repeated cyclically until gasification and filling reach the top of the coal seam.

[0014] Furthermore, the startup sequence of each gasifier is configured such that when any one or more gasifiers are started or running, the gasifiers adjacent to them on both sides are in an ungasified state or have completed maintenance and formed an artificial isolation support zone.

[0015] Furthermore, the maintenance specifically involves: replenishing water into the filling body through the vertical well and maintaining pressure, with the pressure difference between the maintaining pressure and the pressure during gasification filling being ±0.5MPa, and the maintenance time being no less than 28 days.

[0016] Furthermore, before starting maintenance, the ratio of the volume of the filling material brought in by the gasifying agent to the volume of the combustion gob formed by the gasified coal seam is calculated. If the ratio is less than 70%, filling material is added to the combustion gob.

[0017] Furthermore, the mass of the packing material carried by the gasifying agent is 40% to 90% of the mass of the coal to be burned by the gasifying agent.

[0018] Furthermore, the main components of the filling material include 65% to 75% fly ash and 25% to 35% silicate cement by mass.

[0019] Alternatively, it can consist of 60% to 80% fly ash, 15% to 35% quicklime, and 0% to 5% sulfates by weight.

[0020] Furthermore, the filling material also includes auxiliary materials, which include one or more of fine sand, clay, and waste slag, and the proportion of auxiliary materials added is less than one-third of the total mass of the main material.

[0021] On the other hand, an underground gasification furnace system for deep ultra-thick coal seams is provided, applied to the above method, including multiple gasification furnace units arranged in rows, each gasification furnace unit including multiple vertical shafts, and the bottoms of each vertical shaft are interconnected, the vertical shafts extending from the ground to the coal seam;

[0022] In this gasifier unit, multiple vertical wells are configured to switch between injection and outlet functions, alternating as injection holes for injecting the gasifying agent carrying the packing material and outlet holes for collecting the produced gas.

[0023] Furthermore, the horizontal distance between two adjacent gasifier units is 20 to 60 meters.

[0024] The advantages and technical effects of this invention are as follows: By adopting the above-mentioned technical solution, through the synergistic effect of synchronous gasification filling, dynamic adjustment of inlet and outlet gas vents, and in-situ maintenance of artificial isolation support belts, the defects of existing technologies, such as easy collapse of overlying strata in the combustion zone, high risk of stratum subsidence, low coal seam mining rate, high difficulty in regulation, and low thermal energy utilization efficiency, are systematically solved. No pre-reserved support pillars are required. While achieving near-full mining of ultra-thick coal seams, the high-strength support system constructed in situ ensures the stability of the stratum structure, providing an efficient and safe technical path for the large-scale, industrialized underground gasification mining of deep coal resources. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the layout of the underground gasification furnace system provided in an embodiment of the present invention.

[0026] Figure 2 This is a schematic diagram of gasification filling inside the gasifier provided in an embodiment of the present invention.

[0027] Figure 3 This is a complete schematic diagram of the gasification and filling process in the gasifier provided in an embodiment of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] It should be noted that the terms "upper", "lower", "left", "right", "top", "bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0030] like Figure 1 As shown, this application provides an underground gasification furnace system for deep, ultra-thick coal seams, comprising multiple gasification furnace units arranged in rows. Each gasification furnace unit includes multiple vertical shafts, and the bottoms of each vertical shaft are interconnected, extending from the ground surface to the coal seam. The interconnection of the bottoms of the vertical shafts can be achieved using directional drilling technology or other methods.

[0031] In this gasifier unit, multiple vertical wells are configured to switch between injection and outlet functions, alternating as injection holes for injecting the gasifying agent carrying the packing material and outlet holes for collecting the produced gas.

[0032] As a preferred embodiment, the horizontal distance between two adjacent gasifier units is 20 to 60 meters. The horizontal distance from the line connecting multiple vertical shafts within several gasifiers to the line connecting multiple vertical shafts within adjacent gasifiers is 20 to 60 meters.

[0033] To better understand the technical solution, the following will combine... Figure 1 In a non-limiting manner, multiple gasifiers, such as A1~A4, B1~B4, ..., H1~H4, are constructed by drilling into deep underground coal seams. The bottoms of multiple vertical shafts within each gasifier are connected. Gasifying agent carrying filling material is injected through one vertical shaft (e.g., A1) or multiple vertical shafts (e.g., A2 and A4) within a single gasifier, while the remaining vertical shafts serve as gas outlets.

[0034] As an alternative, the horizontally adjacent vertical shafts in two adjacent gasifier units are interconnected. (Combined with...) Figure 1 For example, if the bottoms of A1 to H1 are connected, the gasification combustion can be guided to expand laterally to a single gasifier. For instance, when gasifying B1-B4, gas is produced through the boreholes on the connected A or C columns, and the combustion zone will expand in the direction of A or C columns.

[0035] like Figures 1 to 3 As shown, another aspect provides a method for underground gasification mining of deep, ultra-thick coal seams, including the following steps:

[0036] Multiple gasifiers are constructed in the coal seam. Each gasifier includes multiple vertical shafts and channels that run through the bottom of each vertical shaft. At least one of the multiple vertical shafts is an injection hole, and the rest are outlet holes for collecting the produced coal gas.

[0037] A gasifying agent carrying filling material is injected into the injection hole of the gasifier to cause the coal seam to undergo a gasification reaction and simultaneously fill the resulting combustion air zone.

[0038] The filling material in the gasification and filling zone is cured to solidify it into a whole with supporting strength, forming an artificial isolation support zone. Specifically, the strength of the artificial isolation support zone is greater than or equal to the compressive strength of the coal seam at that location.

[0039] In the gasification process, the functions of the injection holes and outlet holes in a single gasifier are switched according to the volume changes at different locations in the combustion zone. That is, gas is discharged from the original injection holes, and gasifying agent carrying filling material is injected into the original outlet holes, so that the top shape of the combustion zone expands evenly in the direction of coal seam height.

[0040] To better understand the technical solution, the following will combine... Figures 1 to 3 This is a non-limiting description. Multiple gasifiers, such as A1~A4, B1~B4, ..., H1~H4, are constructed by drilling into deep underground coal seams. The bottoms of multiple vertical shafts within each gasifier are connected. Gasifying agent carrying filling material is injected through one or more vertical shafts (e.g., A1) within a single gasifier (e.g., A2 and A4) as injection holes, while the remaining vertical shafts serve as outlet holes. During the gasification and filling operation of this gasifier, a portion of the combustion goaf is occupied by the filling material. The heat energy generated by coal gasification is mainly transferred in the remaining space of the combustion goaf, reducing heat loss. Simultaneously, the smaller remaining space in the combustion goaf minimizes creep and collapse of the sidewall coal seam, significantly reducing the probability of large-scale caving of the overlying strata.

[0041] After gasification for a period of time, compared with the combustion air zone at the gas outlet, the combustion air zone formed at the injection point is relatively wider, higher, and larger in volume, with more deposited filling material. To maintain a relatively consistent coal seam height at the top of the combustion air zone and facilitate gasification filling control, the functions of the injection and outlet holes in the gasifier are swapped. That is, gas is discharged through the original injection hole, and the original outlet hole is used to inject the gasifying agent carrying the filling material. After further gasification and filling for a period of time, the functions of the injection and outlet holes are swapped again until gasification and filling reach the top of the coal seam. In this way, the gasifier (e.g., Figure 1 Within a certain width (e.g., the gasifiers containing B1~B4 in the gasifier) Figure 1 The coal seam covered by the dashed box has almost completely gasified.

[0042] The filling material in the combustion zone is cured to solidify it into a large block or a whole with a certain strength. The solidified filling material can act as an isolation support zone. When the coal seam on both sides is gasified, it plays a role in supporting the overlying rock strata of the coal seam and preventing large-scale collapse of the overlying rock strata, thereby improving the coal seam mining rate.

[0043] Based on the volume changes at different locations within the combustion air zone, the functions of the injection and outlet ports in a single gasifier are adjusted. Specifically, when the volume of the combustion air zone formed at the injection location is greater than the volume of the combustion air zone formed at the outlet location, the functions of the injection and outlet ports within the gasifier are adjusted. This adjustment operation is repeated cyclically until gasification and filling reach the top of the coal seam. It should be noted that the injection location refers to the area within the coal seam where the gasifying agent is injected during the gasification reaction, and the outlet location refers to the area within the coal seam where the syngas is discharged during the gasification reaction.

[0044] The above-mentioned switching operation is based on empirical estimation of the amount of coal consumed and the expansion law of the combustion zone. If the height difference between the highest and lowest points of the combustion zone is greater than or equal to a certain preset value, and / or if the total effective component content of the gas in the vent hole decreases by more than 5%, a switching operation is required. For example, if the height difference between the highest and lowest points of the combustion zone is estimated to be greater than or equal to 2 meters, and / or the average total effective component content of the gas is 35% within 12 hours, and after a 24-hour interval, the average total effective component content of the gas decreases to below 30% within 12 hours, then a switching operation is required.

[0045] To prevent two adjacent gasification zones from connecting due to insufficient support strength, and to avoid large-scale subsidence of the overlying strata caused by excessively large gasification zone spans, as a preferred scheme, the startup sequence of each gasifier is configured as follows: when any one or more gasifiers are started or running, the adjacent gasifiers on both sides are in an ungasified state or have completed curing, forming an artificial isolation support zone. Specifically, with Figure 1 Taking the example shown, during the operation or maintenance of the gasifiers located in vertical shafts A1~A4, the gasifiers located in vertical shafts C1~C4 can be started, while the gasifiers located in vertical shafts B1~B4 are not operated. Alternatively, the gasifiers located in vertical shafts B1~B4 and D1~D4 can be operated simultaneously. When both are in the process of gasification or maintenance, the gasifiers located in vertical shafts F1~F4 and H1~H4 can be started. When the gasifiers located in vertical shafts F1~F4 and H1~H4 are undergoing maintenance, the gasifiers located in vertical shafts A1~A4 and C1~C4 can be started, at which point the gasifiers located in vertical shafts B1~B4 and D1~D4 have already completed their maintenance. Never start a gasifier that is gasifying or under maintenance next to another gasifier. If one gasifier is started while the adjacent gasifier is in a gasification or maintenance state, the supporting strength of the packing material in the adjacent gasifier is not high. Once the newly started gasifier has been running for a period of time, its combustion zone will expand and may connect with the combustion zone of the adjacent gasifier, causing a large-scale collapse of the overlying rock strata in the larger combustion zone and resulting in ground subsidence.

[0046] Furthermore, the maintenance specifically involves: replenishing water into the filling body through the vertical well and maintaining pressure, with the pressure difference between the maintaining pressure and the pressure during gasification filling being ±0.5MPa, and the maintenance time being no less than 28 days.

[0047] This curing process is similar to the consolidation curing of the filling material on the surface, except that the conditions in the underground combustion chamber are relatively less strictly controlled. The filling material injected along with the gasifying agent is in dry powder form, and it still settles as powder in the combustion chamber. Consolidation requires the addition of water. Typically, after the gasifier stops operating (pressure is released), groundwater will gradually (over a long period) flow into the combustion chamber. To control the consolidation of the filling material, water is injected into the filling material (to match the consolidation of the filling material) to maintain pressure and prevent groundwater from flowing into the filling material (which would cause the water required for the consolidation of the filling material to be inaccurately replenished). The mass of the replenished water is less than or equal to 20% of the total mass of the filling material.

[0048] As a preferred option, before starting maintenance, the ratio of the volume of the filling material brought in by the gasifying agent to the volume of the combustion goaf formed by the gasified coal seam is calculated. If the ratio is less than 70%, filling material is added to the combustion goaf.

[0049] As a preferred embodiment, to ensure that the remaining space after the underground combustion chamber is filled is neither too small nor too large, it is crucial to avoid situations where the space is too small, as this can easily lead to blockage of the gasification channels and shutdown of the gasifier, or excessively high gasification agent flow rates that may result in low effective component content in the gasified coal gas. Conversely, excessive remaining space can lead to significant heat loss and low gasification efficiency of the gasifier. Therefore, the mass of the packing material carried by the gasification agent is 40% to 90% of the mass of the coal to be burned. Preferably, it is 60% to 80%.

[0050] In the above, the filling material can be fly ash and silicate cement, or a mixture of fly ash, quicklime and sulfate.

[0051] Specifically, the main components of the filling material include 65% to 75% fly ash and 25% to 35% silicate cement by mass.

[0052] Alternatively, the composition may consist of 60%–80% fly ash, 15%–35% quicklime, and 0%–5% sulfate. Sodium sulfate is preferred as the sulfate. The fly ash should be screened so that over 90% of the particles are below 0.3 mm in diameter.

[0053] Table 1 shows the comparison of flexural strength and compressive strength of specimens made from fillers with different proportions after a period of curing.

[0054] Table 1 Comparison of performance of compressed molded parts with different filler ratios

[0055] Furthermore, the filling material also includes auxiliary materials, which include one or more of fine sand, clay, and waste slag, and the proportion of auxiliary materials added is less than one-third of the total mass of the main material. Adding auxiliary materials will not significantly reduce the performance of the filling material, reduce the amount of main material used, and can also handle some waste, such as waste slag.

[0056] By employing the aforementioned technical solution, through the synergistic effects of synchronous gasification filling, dynamic adjustment of inlet and outlet gas vents, and in-situ maintenance of artificial isolation support zones, the shortcomings of existing technologies, such as easy collapse of overlying strata in the combustion zone, high risk of stratum subsidence, low coal seam mining rate, difficulty in regulation, and low thermal energy utilization efficiency, are systematically solved. No pre-reserved support pillars are required. While achieving near-full mining of ultra-thick coal seams, the high-strength support system constructed in situ ensures the stability of the stratum structure, providing an efficient and safe technical path for the large-scale, industrialized underground gasification mining of deep coal resources.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for underground gasification extraction of deep, ultra-thick coal seams, characterized in that, Includes the following steps: Multiple gasifiers are constructed in the coal seam. Each gasifier includes multiple vertical shafts and a channel that runs through the bottom of each vertical shaft. At least one of the multiple vertical shafts is an injection hole, and the rest are gas outlet holes for collecting the produced coal gas. A gasifying agent carrying filling material is injected into the injection hole of the gasifier to cause the coal seam to undergo a gasification reaction and to simultaneously fill the resulting combustion air zone. The filling material in the gasification and filling zone is cured to solidify it into a whole with supporting strength, so as to form an artificial isolation support zone. In the gasification process, the functions of the injection holes and exhaust holes in a single gasifier are adjusted according to the volume changes at different locations in the combustion zone, so that the top morphology of the combustion zone expands uniformly in the direction of coal seam height.

2. The method for underground gasification mining of deep, ultra-thick coal seams according to claim 1, characterized in that, Based on the volume changes at different locations in the combustion zone, the functions of the injection holes and outlet holes in a single gasifier are adjusted as follows: when the volume of the combustion zone formed at the injection position is greater than the volume of the combustion zone formed at the outlet position, the functions of the injection holes and outlet holes in the gasifier are adjusted; and the adjustment operation is repeated cyclically until gasification and filling reach the top of the coal seam.

3. The method for underground gasification extraction of deep, ultra-thick coal seams according to claim 1, characterized in that, The startup sequence of each gasifier is configured such that when any one or more gasifiers are started or running, the gasifiers on both sides of them are in an ungasified state or have completed maintenance and formed an artificial isolation support zone.

4. The method for underground gasification mining of deep, ultra-thick coal seams according to claim 1, characterized in that, The maintenance process specifically involves replenishing water into the filling body through the vertical well and maintaining pressure. The pressure difference between the pressure maintained and the pressure during gasification filling is ±0.5 MPa, and the maintenance time is no less than 28 days.

5. The method for underground gasification mining of deep, ultra-thick coal seams according to claim 1, characterized in that, Before starting the curing process, calculate the ratio of the volume of the filling material brought in by the gasifying agent to the volume of the combustion gob formed by the gasified coal seam. If the ratio is less than 70%, then filler material is added to the combustion gob.

6. The method for underground gasification mining of deep, ultra-thick coal seams according to claim 1, characterized in that, The mass of the packing material carried by the gasifying agent is 40% to 90% of the mass of the coal to be burned.

7. The method for underground gasification mining of deep, ultra-thick coal seams according to claim 1, characterized in that, The main components of the filling material include 65% to 75% fly ash and 25% to 35% silicate cement by mass. Alternatively, it can consist of 60% to 80% fly ash, 15% to 35% quicklime, and 0% to 5% sulfates by weight.

8. The method for underground gasification mining of deep, ultra-thick coal seams according to claim 7, characterized in that, The filling material also includes auxiliary materials, which include one or more of fine sand, clay, and waste slag, and the proportion of auxiliary materials added is less than one-third of the total mass of the main material.

9. An underground gasification furnace system for deep, ultra-thick coal seams, applied to the method described in any one of claims 1 to 8, characterized in that, It includes multiple gasifier units arranged in rows, each gasifier unit including multiple vertical shafts, and the bottoms of each vertical shaft are interconnected, the vertical shafts extending from the ground to the coal seam; In this gasifier unit, multiple vertical wells are configured to switch between injection and outlet functions, alternating as injection holes for injecting the gasifying agent carrying the packing material and outlet holes for collecting the produced gas.

10. The underground gasification furnace system according to claim 9, characterized in that, The horizontal distance between two adjacent gasifier units is 20 to 60 meters.

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