A safe ignition method for underground in-situ gasification of coal in a high-gas coal seam

Abstract

The present application relates to the technical field of coal underground in-situ gasification, and particularly relates to a high-gas coal seam coal underground in-situ gasification safety ignition method. The present application accurately divides the ignition area based on the length, width and coal seam thickness of the gasification channel; meanwhile, the present application adopts a double-monitoring-unit setting mode of the ignition area and the gas transmission direction to realize blind area-free monitoring of the gasification channel, which not only meets the partition monitoring requirement, but also guarantees the continuity and accuracy of parameter collection, and provides reliable data support for subsequent gasification channel pressure maintenance, purging and ignition point selection. The present application adopts gas introduction for pressure maintenance treatment in the gasification channel, so that the gas adsorbed in the coal seam fissures can be separated out and mixed with air, and the distribution of the gas in the whole channel and the surrounding fissure network is more uniform; meanwhile, the gasification channel is purged after pressure maintenance, so that the gas in the gasification channel can be quickly discharged, and the efficiency of gas discharge is increased.

Description

Technical Field

[0001] This invention relates to the field of underground in-situ coal gasification technology, and in particular to a safe ignition method for underground in-situ coal gasification in high-gas coal seams. Background Technology

[0002] In-situ underground coal gasification is a highly promising method for coal resource development, but its implementation in high-gas coal seams faces severe challenges. Due to the characteristics of high-gas coal seams, such as easy gas accumulation, unbalanced pressure distribution, and complex geological conditions, it is necessary to completely vent the gas before igniting the coal to reduce the gas concentration to a safe range.

[0003] Currently, the common method for gas emission from coal seams is to use negative pressure extraction. However, the underground in-situ environment contains a large number of fissures and pores, and gas tends to accumulate and flow in these complex channels. At the same time, gas can also be adsorbed in the fissures of the coal seam, resulting in a long time consumption for current gas emission methods.

[0004] In addition, the existing technology has the following shortcomings in the in-situ gasification ignition process of high-gas coal seams: (1) The existing monitoring scheme is not reasonably set up, or only monitors local areas, or does not combine the ignition area zoning requirements, resulting in monitoring blind spots for key parameters such as gas concentration and gas pressure in the gasification channel.

[0005] (2) The gas extraction process uses a single extraction pressure to extract gas. This method is prone to the gas adsorbed in the coal seam fissures or voids not being fully extracted, which leads to gas outbursts and increased gas concentration in the later stage, causing safety hazards. At the same time, the gas extraction is stopped only by judging the gas concentration, without considering the risk of gas rebound.

[0006] (3) The determination of the coal seam ignition point is based on experience and does not take into account the gasification channel structure parameters and airflow characteristics. It does not avoid the airflow turbulence zone near the air inlet, which is prone to increase the ignition risk due to gas accumulation or airflow fluctuation in the area. At the same time, it does not take into account the influence factors such as channel curvature, inclination, and gas mixing effect, resulting in uneven combustion propagation and low gasification efficiency after ignition. Summary of the Invention

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a safe ignition method for underground in-situ gasification of coal in high-gas coal seams, comprising: injecting air into the gasification channel, and acquiring pressure holding parameters at each location through multiple monitoring units set in the gasification channel.

[0008] Based on the pressure holding parameters, it is determined whether the vaporization channel meets the stable pressure holding state, and if it does, pressure holding treatment is performed on the gas in the channel.

[0009] After the pressure holding process is completed, air is introduced into the vaporization channel for purging, and the air pressure and gas concentration at each location are acquired at monitoring times during the purging process.

[0010] Based on the gas pressure and gas concentration, the purging performance coefficient is analyzed, and the flow rate of the incoming air is adjusted according to the purging performance coefficient until the gas concentration at the outlet of the vaporization channel drops below the safety standard and then the purging is stopped.

[0011] The ignition zone is determined based on the layout parameters of the gasification channel, and the ignition zone is divided into several sub-regions along the coal seam direction.

[0012] The operating parameters of the gasification channel are obtained, and each sub-region is comprehensively scored based on the operating parameters. The sub-region with the highest score is selected as the ignition point for in-situ underground gasification of the coal seam.

[0013] Furthermore, the monitoring unit is configured such that one monitoring unit is set up in each sub-region of the ignition area.

[0014] Several monitoring units are evenly arranged along the gas transmission direction of the gasification channel.

[0015] The monitoring unit is used to monitor the air pressure and gas concentration at the installation location.

[0016] Furthermore, the judgment conditions for performing pressure holding treatment on the gas in the vaporization channel are as follows: during the process of injecting air into the vaporization channel, the pressure value at each position is acquired in real time, the average value of the pressure value at each position is calculated, and the pressure deviation at each position is analyzed; for each monitoring position, the absolute deviation between its pressure value and the average value is calculated, and the ratio of the absolute deviation to the average value is taken as the pressure deviation at that monitoring position.

[0017] Set the pressure holding threshold range and maximum allowable deviation of the vaporization channel.

[0018] When the average pressure is within the set pressure holding threshold range, and the pressure deviation of all monitoring positions is less than or equal to the maximum allowable deviation, and this continues for a preset duration, the vaporization channel is determined to be in a suitable pressure holding state, and the gas in the vaporization channel is pressure held at the current pressure.

[0019] Furthermore, when the pressure deviation at each location exceeds the preset value, it is necessary to analyze the leakage point of the vaporization channel. The specific analysis method is as follows: calculate the difference between the real-time pressure value and the average pressure value of each monitoring unit to obtain the pressure residual at each monitoring location.

[0020] All pressure residuals are statistically analyzed, and monitoring locations where the absolute value of the residual exceeds a preset deviation threshold are selected and recorded as pressure anomaly monitoring locations.

[0021] The spatial distribution of the pressure anomaly monitoring location within the vaporization channel is read. When the pressure residual between adjacent monitoring locations of the pressure anomaly monitoring location shows a continuous increasing or decreasing trend, it is determined that there is a leakage channel in the channel section corresponding to the starting monitoring location to the ending monitoring location of the pressure anomaly monitoring location, and this channel section is recorded as the pressure leakage zone.

[0022] The pressure leakage area is scanned to determine the specific coordinates of the leakage point and the size of the leakage hole, and then the leakage is sealed with sealing material.

[0023] Furthermore, the specific analysis method for the purging performance coefficient is as follows: at each monitoring moment, the air pressure and gas concentration at each monitoring location are obtained.

[0024] Gradient analysis is performed on the gas concentration at each monitoring location and the gas concentration at adjacent monitoring locations to obtain the gas gradient coefficient at each monitoring location. The average gradient coefficient is then calculated by averaging the gas gradient coefficients.

[0025] Based on the air pressure analysis of each monitoring location, the air pressure fluctuation values ​​are normalized and converted into an air pressure influence coefficient between 0 and 1.

[0026] The average gradient coefficient and the average pressure influence coefficient are linearly weighted to obtain the purging performance coefficient.

[0027] Furthermore, the criteria for determining whether to adjust the airflow based on the purging performance coefficient are as follows: if the purging performance coefficient is greater than or equal to the set qualified threshold, the purging effect is considered good, and the current airflow is maintained.

[0028] If the purging performance coefficient is less than the acceptable threshold, the airflow rate needs to be increased.

[0029] Furthermore, the criterion for stopping purging is as follows: read the gas concentration collected at the monitoring location near the gasification channel outlet and analyze the gas fluctuation rate at each monitoring moment.

[0030] When the gas concentration monitored at the monitoring location is less than or equal to the safety standard, the gas fluctuation rate of the previous monitoring time is read, and the gas compensation rate is calculated.

[0031] The gas concentration compensation amount is obtained by multiplying the gas safety standard value and the gas compensation rate. The difference between the gas safety standard value and the gas concentration compensation amount is taken as the final safe gas concentration.

[0032] When the gas concentration at the monitoring location is lower than the final safe gas concentration, the purging process is stopped.

[0033] Furthermore, the specific analysis method for the ignition area is as follows: obtain the parameters of the direction length, channel width, and coal seam thickness of the gasification channel.

[0034] The midpoint of the stated direction length is taken as the end boundary of the ignition region.

[0035] Starting from the gas inlet of the gasification channel, a predetermined safe distance is extended inward along the direction of the gasification channel, and the end point of the extension is taken as the starting boundary of the ignition area; wherein, the safe distance is determined based on the channel width and the coal seam thickness.

[0036] The vaporization channel section between the starting boundary and the ending boundary is designated as the ignition zone.

[0037] Furthermore, the parameters considered in the comprehensive scoring of each sub-region based on the aforementioned operating conditions include: the curvature of the channel segment where the sub-region is located, the inclination angle relative to the horizontal plane, the distance to the gas injection point, and the geological conditions of the coal seam in that region; the specific analysis method is as follows: read the curvature radius of each sub-region in the ignition area, filter the sub-region with the maximum curvature radius, record the curvature parameter of that sub-region as 1, and the curvature parameter of the remaining sub-regions is the ratio of the curvature radius of the corresponding sub-region to the maximum curvature radius.

[0038] Read the tilt of each sub-region in the ignition area, filter the sub-regions whose tilt is within the optimal tilt range, and record their tilt parameter as 1. The tilt parameter of the remaining sub-regions is calculated by: calculating the deviation between the tilt and the optimal tilt range, and using the difference between 1 and the deviation as the tilt parameter.

[0039] The area within the set distance from the air inlet is defined as the optimal mixing region. The position parameters of each sub-region located in the optimal mixing region are recorded as 1, and the position parameters of the remaining sub-regions are determined by using the tilt parameter analysis method.

[0040] A comprehensive score is obtained by analyzing the curvature parameters, tilt parameters, and position parameters of each sub-region.

[0041] Furthermore, the specific analysis method for the ignition point is as follows: the comprehensive score of each sub-region is calculated by linear weighting based on the curvature parameters, tilt parameters and position parameters of each sub-region; and the comprehensive scores of all sub-regions are sorted in descending order, and the sub-region with the highest score is selected as the ignition point for in-situ gasification of the coal seam.

[0042] The beneficial effects of this system are as follows: First, based on data such as the direction length, width, and coal seam thickness of the gasification channel, this invention accurately divides the ignition zone; at the same time, this invention avoids unstable areas at the air inlet by maintaining a safe distance, and ensures the effective length of the ignition zone by using the midpoint as the boundary; thus, it directly provides a basic range for the deployment of monitoring units and the selection of ignition points; furthermore, this invention adopts a dual monitoring unit setting method for the ignition zone and the gas transmission direction, realizing blind-spot-free monitoring of the gasification channel, which not only meets the requirements of zoned monitoring, but also ensures the continuity and accuracy of parameter acquisition, providing reliable data support for subsequent gasification channel pressure maintenance, purging, and ignition point selection.

[0043] Second, unlike traditional methods that use a fixed negative pressure to extract gas, this invention employs a pressure-maintaining process by introducing gas into the gasification channel. This allows gas adsorbed within coal seam fissures to be released and mixed with air, resulting in a more uniform gas distribution throughout the channel and surrounding fissure network. Simultaneously, the gasification channel is purged after pressure maintenance, enabling rapid gas discharge and improving emission efficiency. The pressure maintenance process incorporates dual criteria: average pressure and pressure deviation. This not only accurately determines a stable pressure state but also allows for rapid location of leaks and their diameters through pressure residual trend analysis, enabling early sealing to eliminate safety hazards and prevent gas leakage and pressure imbalance.

[0044] Third, this invention constructs a purging performance coefficient by using the gas gradient coefficient and the air pressure influence coefficient, thereby achieving a quantitative evaluation of the purging effect. It can dynamically adjust the airflow to adapt to different purging scenarios, and calculate the compensation rate based on the gas fluctuation rate to set the final safe concentration, thereby avoiding gas rebound and accumulation after purging and ensuring the thoroughness of gas purging.

[0045] Fourth, this invention integrates multiple parameters such as channel curvature, inclination, and distance from the injection point, and uses a linear weighting method to calculate the comprehensive score of the sub-region, accurately selecting the optimal ignition point, ensuring smooth airflow and sufficient gas mixing after ignition, and improving combustion stability and gasification efficiency. Attached Figure Description

[0046] The present invention will be further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the present invention. For those skilled in the art, other drawings can be obtained based on the following drawings without creative effort.

[0047] Figure 1 This is a flowchart of the safe ignition method for underground in-situ gasification of coal according to the present invention. Detailed Implementation

[0048] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or in accordance with the product manual.

[0049] See Figure 1 A safe ignition method for underground in-situ gasification of coal in high-gas coal seams includes the following steps: S10, injecting air into the gasification channel and acquiring pressure holding parameters at each location through multiple monitoring units installed in the gasification channel.

[0050] In embodiments of the present invention, in-situ underground gasification of high-gas coal seams requires the layout and excavation of gasification channels. This involves employing geological exploration techniques such as 3D seismic exploration and core drilling analysis to thoroughly understand the geological structure, gas distribution patterns, permeability, and porosity of the high-gas coal seam. Based on the exploration results, the optimal layout scheme for the gasification channels is determined, including the channel direction, length, diameter, and relationship with surrounding geological structures. The design of the gasification channels is prior art and not part of the inventive concept of this invention; therefore, it will not be elaborated upon further.

[0051] Simultaneously, air inlets and outlets are opened on both sides of the gasification channel. The air inlets are used for initial discharge of coalbed methane and injection of air, and during coal gasification, they introduce gases such as air, water vapor, and nitrogen to assist in coal gasification. The air outlets are used for initial methane discharge and for collecting the final mixture of coal gas and other gases produced during coal gasification. In addition, auxiliary equipment for coal gas purification is also installed at the air outlets. Gas collection and purification in in-situ coal gasification is existing technology and will not be elaborated upon here.

[0052] Considering that during the in-situ underground gasification of high-gas coal seams, the gas concentration in the gasification channel is prone to accumulation and the pressure distribution is prone to imbalance, improper deployment of monitoring units can lead to blind spots in the monitoring of key parameters, resulting in safety hazards such as misjudgment of pressure holding, omission of leak points, incomplete purging, or improper selection of ignition points. Therefore, setting the configuration method of monitoring units is a prerequisite for ensuring ignition safety.

[0053] Before setting up the monitoring unit, it is necessary to analyze the ignition area of ​​the gasification channel. The purpose of the ignition area is to avoid areas with turbulent airflow and gas accumulation risk, so as to provide accurate basis for the subsequent deployment of monitoring units and selection of ignition points, and avoid safety accidents such as ignition explosion and incomplete combustion caused by improper area delineation.

[0054] In an embodiment of the present invention, S11, the ignition area is determined according to the arrangement parameters of the gasification channel, and the ignition area is divided into several sub-regions along the coal seam direction.

[0055] Considering that the gas concentration distribution is most balanced at the midpoint of the gasification channel and the airflow stability is better than at both ends, the risk of ignition caused by local gas enrichment or airflow fluctuations can be avoided. Therefore, the midpoint of the gasification channel is taken as the end boundary of the ignition zone.

[0056] In principle, the closer the starting boundary of the ignition zone is to the air inlet, the better. This is because coal seam gasification is most favorable when it is carried out sequentially according to the direction of the coal seam. At the same time, the air inlet is the gas injection end, and the airflow speed is fast and the pressure fluctuation is large in the vicinity. The unstable period of gas desorption and airflow mixing is long. It is necessary to avoid the port position of the air inlet. That is, extending a certain safe distance can avoid this turbulent zone and ensure that the airflow and gas concentration in the ignition zone are in a stable state.

[0057] In an embodiment of the present invention, the specific analysis method of the ignition area is as follows: obtain the parameters of the direction length, channel width and coal seam thickness of the gasification channel.

[0058] The midpoint of the stated direction length is taken as the end boundary of the ignition region.

[0059] Starting from the air inlet of the gasification channel, a predetermined safe distance is extended inward along the direction of the gasification channel, and the endpoint of the extension is taken as the starting boundary of the ignition area. The safe distance is determined based on the channel width and the coal seam thickness. The channel width determines the airflow diffusion range. The wider the channel, the slower the airflow diffusion and the wider the unstable zone. The coal seam thickness is positively correlated with the gas storage capacity and the gasification time. Therefore, the gasification channel width and the coal seam thickness together determine the actual range of the unstable zone.

[0060] The vaporization channel section between the starting boundary and the ending boundary is designated as the ignition zone.

[0061] It should be noted that the safety distance is determined based on statistical analysis of historical engineering data. The specific steps are as follows: obtain historical parameter sets of multiple successfully implemented high-gas coal seam underground in-situ gasification projects. Each parameter set includes the actual width of the gasification channel, the coal seam thickness, and the corresponding safety distance.

[0062] From the historical parameter set, a subset of data was selected that satisfies the requirement that the relative deviation between the actual width of the gasification channel and the design width of the target gasification channel is less than or equal to 10%, and the relative deviation between the coal seam thickness and the coal seam thickness of the target gasification channel is less than or equal to 10%.

[0063] Calculate the 25th percentile and 75th percentile of all safe distances in the data subset to form a threshold interval [25th percentile, 75th percentile], and select the median value of this threshold interval as the safe distance.

[0064] Based on data such as the direction length, width, and coal seam thickness of the gasification channel, this invention can objectively and accurately divide the ignition zone. At the same time, this invention avoids the unstable area of ​​the air inlet by maintaining a safe distance and ensures the effective length of the ignition zone by using the midpoint as the boundary. Thus, it directly provides a basic range for the deployment of monitoring units and the selection of ignition points.

[0065] In an embodiment of the present invention, S12, the monitoring unit is configured such that one monitoring unit is provided in each sub-region of the ignition area.

[0066] Several monitoring units are evenly arranged along the gas transmission direction of the gasification channel.

[0067] The pressure-holding parameters include gas pressure and gas concentration.

[0068] The monitoring unit is used to monitor the gas pressure and gas concentration at the installation location. It is understood that monitoring of gas pressure and gas concentration within the gasification channel can be achieved using appropriate sensors; this monitoring method is existing technology and will not be elaborated upon here.

[0069] The monitoring unit of this invention adopts the above-mentioned dual deployment method, which can fully cover the gasification channel without blind spots. At the same time, combined with the division of each sub-region of the ignition area and the uniform deployment in the gas transmission direction, it can both take into account the zonal monitoring needs of the ignition area and ensure the continuous acquisition of parameters of the entire channel.

[0070] In addition, the monitoring unit integrates multi-parameter monitoring functions, which can simultaneously acquire gas pressure and gas concentration. At the same time, the deployment location and monitoring parameters are precisely matched to the needs of subsequent core processes such as pressure holding, purging, and ignition point selection.

[0071] S20, based on the pressure holding parameters, determine whether the gasification channel meets the stable pressure holding state, and perform pressure holding treatment on the gas in the channel after it meets the requirements.

[0072] It is important to emphasize that the gasification channel is isolated from the surrounding environment using drilling and sealing techniques. Air is then injected into the channel. During the injection process, the pressure inside the channel gradually increases, driving the gas to the channel edges and surrounding fissures, where it mixes with the air. This results in a more uniform gas distribution, achieving "pressure buildup" within the gasification channel. Furthermore, the pressure-maintaining process facilitates the release of gas adsorbed within the coal seam, enhancing the subsequent gas emission effect.

[0073] Considering that the air injection rate in the gasification channel needs to be determined according to the pressure in the gasification channel, it is necessary to avoid sudden pressure changes that could cause damage to the coal seam structure or abnormal gas outbursts.

[0074] Furthermore, considering that the gasification channels in high-gas coal seams are located in complex geological environments, they are prone to problems such as fissures and poor sealing at interfaces, leading to gas leakage. At the same time, uneven pressure distribution at various locations during air injection can affect gas replacement efficiency. If pressure-holding criteria are not established, channel leaks may go undetected, resulting in gas leaks and safety accidents. Additionally, if subsequent processes are carried out before the pressure reaches the required level, turbulent airflow during purging will prevent the complete removal of gas.

[0075] Therefore, in the embodiment of the present invention, S21, the judgment condition for the gas in the vaporization channel to perform pressure holding treatment is as follows: during the process of injecting air into the vaporization channel, the pressure value at each position is acquired in real time, the average value of the pressure value at each position is calculated, and the pressure deviation at each position is analyzed; for each monitoring position, the absolute deviation between its pressure value and the average value is calculated, and the ratio of the absolute deviation to the average value is used as the pressure deviation at that monitoring position.

[0076] Set the pressure holding threshold range and maximum allowable deviation of the vaporization channel.

[0077] If the average pressure and the pressure deviation both meet the following conditions, the vaporization channel is determined to be in a suitable pressure-holding state, and the gas in the vaporization channel is pressure-held at the current pressure.

[0078] Condition 1: The average pressure is within the set pressure holding threshold range.

[0079] Condition 2: The pressure deviation at all monitoring locations is less than or equal to the maximum permissible deviation, and this condition is maintained for a preset duration.

[0080] The pressure holding threshold range for the gasification channel is typically 2MPa-4MPa; the maximum permissible deviation is generally set at 8%-15%. The lower limit of the maximum permissible deviation is suitable for scenarios with good channel integrity and high sealing requirements, ensuring highly uniform pressure distribution and sufficient gas replacement. The upper limit of the maximum permissible deviation is suitable for scenarios with relatively complex geological conditions and in the initial pressure holding stage, where a certain pressure gradient is permissible. The preset duration is set between 10 and 30 minutes. This range ensures that a stable pressure state is captured under most operating conditions while avoiding the impact on project efficiency due to excessive waiting time. In specific implementation, it can be fine-tuned according to the permeability of the coal seam. Coal seams with poor permeability should be closer to the upper limit, and coal seams with good permeability should be closer to the lower limit.

[0081] This invention is based on a dual judgment standard of pressure mean and deviation, avoiding the bias of judgment by a single parameter; at the same time, this invention can detect potential air leakage in advance by using pressure deviation and simultaneously identify the leak point, eliminating safety risks before purging and ignition, and improving the safety and efficiency of subsequent purging and ignition.

[0082] In an embodiment of the present invention, S22, when the pressure deviation at each location exceeds a preset value, it is necessary to analyze the leakage point of the vaporization channel. The specific analysis method is to calculate the difference between the real-time pressure value and the average pressure value of each monitoring unit to obtain the pressure residual at each monitoring location.

[0083] All pressure residuals are statistically analyzed, and monitoring locations where the absolute value of the residual exceeds a preset deviation threshold are selected and recorded as pressure anomaly monitoring locations. Since pressure residuals are not necessarily caused by air leakage in the channel, it is not possible to determine the existence of an air leakage channel at a monitoring location based on a single pressure residual.

[0084] The spatial distribution of the pressure anomaly monitoring location within the vaporization channel is read. When the pressure residual of the adjacent monitoring locations of the pressure anomaly monitoring location shows a continuous increasing or decreasing trend, it is determined that there is a leakage channel in the channel section corresponding to the starting monitoring position to the ending monitoring position of the pressure anomaly monitoring location. This channel section is recorded as a pressure leakage zone. The basis for this determination is that the leakage point will cause changes in the surrounding pressure gradient, forming a continuous trend.

[0085] If the residuals of adjacent points at the abnormal monitoring location show a continuous trend, the abnormal monitoring location and the channel segment corresponding to the adjacent monitoring location covered by the continuous trend are defined as the pressure leakage zone.

[0086] The pressure leakage area is scanned to determine the specific coordinates of the leakage point and the size of the leakage hole, and then the leakage is sealed with sealing material.

[0087] For example, when determining a pressure leak zone, there must be at least one abnormal pressure monitoring location, meaning the absolute value of the pressure residual at that monitoring location is greater than a preset deviation threshold. Simultaneously, among the adjacent monitoring locations to the left and right of the abnormal pressure monitoring location, at least one side must exhibit a continuously increasing or decreasing pressure residual trend. Furthermore, the magnitude of this trend change must exceed 50% of the preset deviation threshold. The range of the pressure leak zone is the channel segment corresponding to the starting and ending monitoring locations of the continuous trend, i.e., from the first adjacent monitoring location showing a trend change to the last adjacent monitoring location showing a trend change, ensuring coverage of the leak point and surrounding potential leak channels.

[0088] It should be noted that for cracks and pores in the pressure leakage area, composite sealing material is used for filling. During the filling process, pressure equipment is used to ensure that the material fully fills and penetrates deep into the crack. For pressure leakage areas located at connection points such as gas injection pipes, metal sealing rings, elastic sealing gaskets, and sealant are installed sequentially, and a sealing performance test is performed after installation.

[0089] The analysis of pressure leakage zones in this invention is based on the pressure residual and trend analysis of the monitoring unit, avoiding the one-sided judgment of a single parameter, thus achieving a high accuracy rate in identifying leakage zones. At the same time, this analysis focuses on abnormal monitoring locations and adjacent areas, eliminating the need for full-channel investigation and improving investigation efficiency.

[0090] S30, after the pressure holding process is completed, air is introduced into the vaporization channel for purging, and the air pressure and gas concentration at each location are acquired at monitoring times during the purging process.

[0091] This invention uses airflow to further dilute and disperse residual gas in the vaporization channel and surrounding fissures, ensuring that the gas is effectively purged and that the airflow in the channel is stable, creating favorable conditions for ignition.

[0092] S40, based on the gas pressure and gas concentration, analyze the purging performance coefficient, and determine whether to adjust the flow rate of the incoming air according to the purging performance coefficient, until the gas concentration at the outlet of the vaporization channel drops below the safety standard and purging is stopped.

[0093] In an embodiment of the present invention, S41, the specific analysis method of the purging performance coefficient is as follows: at each monitoring moment, the air pressure and gas concentration at each monitoring location are obtained.

[0094] The gas concentration at each monitoring location is analyzed for gradient with that at adjacent monitoring locations to obtain the gas gradient coefficient for each monitoring location. The average gradient coefficient is then calculated by averaging the gas gradient coefficients. For example, starting from the monitoring location closest to the air inlet, the locations are sequentially labeled as monitoring location 1, monitoring location 2, ..., monitoring location i, ..., monitoring location n. The absolute value of the difference between the gas concentration at monitoring location i and the gas concentration at monitoring location i+1 is calculated. This absolute value is then compared with the distance between the two monitoring locations to obtain the gas concentration gradient value per unit length at monitoring location i. This gas concentration gradient value per unit length is then compared with the maximum allowable difference in gas concentration per unit length. The difference between 1 and this ratio is taken as the gas gradient coefficient. The average gradient coefficient is then calculated by averaging the gas gradient coefficients at all monitoring locations. A larger average gradient coefficient indicates a higher uniformity of gas concentration.

[0095] The maximum allowable difference in gas concentration per unit length is generally set between 0.005% / m and 0.02% / m. It is determined based on the ratio of the final safe gas concentration to be achieved after purging to the length of the ignition zone in the gasification channel. Physically, this means evenly distributing the total allowable concentration change (i.e., the safe concentration value) across the entire ignition zone to the unit channel length, thus setting a uniformity target for the concentration gradient distribution during purging. For example, if the final safe gas concentration to be achieved after purging is 0.8%, and the length of the ignition zone in the gasification channel is 100m, then the maximum allowable difference in gas concentration per unit length is set to 0.008% / m.

[0096] Based on the air pressure fluctuation values ​​at each monitoring location, the values ​​are normalized and converted into air pressure influence coefficients between 0 and 1. The average air pressure influence coefficient is then calculated by averaging these values. For example, the air pressure fluctuation value at monitoring location i is the absolute value of the difference between the air pressure value at monitoring location i and the air pressure value at monitoring location i+1. The above air pressure influence coefficient analysis uses the Z-Score normalization method for calculation, and the formula is as follows: ,in This represents the air pressure influence coefficient at monitoring location i. This represents the air pressure fluctuation value at a certain monitoring location i. This represents the average value of air pressure fluctuations. The standard deviation of the air pressure fluctuation value at monitoring location i is represented by the average air pressure influence coefficient calculated by averaging the air pressure influence coefficients of all monitoring locations. The larger the average air pressure influence coefficient, the better the air pressure fluctuation at each monitoring location and the better the purging effect.

[0097] The average gradient coefficient and the average gas pressure influence coefficient are linearly weighted to obtain the purging performance coefficient. For example, since the gas concentration is the most important indicator for purging the gasification channel, in this embodiment, the average gradient coefficient has a weight of 0.6 and the average gas pressure influence coefficient has a weight of 0.4.

[0098] This invention analyzes the purging performance coefficient from two aspects by comprehensively analyzing the gas discharge progress and airflow stability, making the analysis of the purging effect of the gasification channel more comprehensive and accurate. At the same time, this invention uses methods such as basic difference, mean and normalization calculation to transform complex multi-parameter monitoring data into intuitive quantitative indicators, providing a basis for dynamic adjustment of purging flow rate. Moreover, this invention monitors and analyzes in real time, and can quickly provide feedback on the adjustment direction.

[0099] S42, the decision on whether to adjust the airflow based on the purging performance coefficient is as follows: if the purging performance coefficient is greater than or equal to the set qualified threshold, the purging effect is determined to be good, and the current airflow is maintained.

[0100] If the purging performance coefficient is between the qualified threshold and the fine-tuning threshold, it indicates that the purging efficiency in a local area is too low, and the air flow rate needs to be increased by 10%-20%.

[0101] If the purging performance coefficient is less than the fine-tuning threshold, it indicates a serious purging blind spot, and the airflow should be increased by 30% immediately.

[0102] It should be noted that the qualified threshold and fine-tuning threshold of this invention can be set with reference to historical data; specifically, they are dynamically adjusted according to the permeability coefficient, original gas pressure, and gasification channel design parameters of high-gas coal seams under different geological conditions. For example, in tight coal seams with low permeability, the qualified threshold can be set to 0.75 and the fine-tuning threshold to 0.55 to ensure that even under conditions of high gas migration resistance, the purging intensity can still be forcibly increased through a higher threshold standard; while for high-permeability coal seams, the qualified threshold can be reduced to 0.65 and the fine-tuning threshold to 0.45 to avoid energy waste caused by excessive purging. Through this threshold setting method that combines geological parameters and field tests, precise control of the purging process can be achieved, ensuring both safety and economy.

[0103] When the gas concentration at the gasification channel outlet drops to the required range, it indicates that the gas concentration has been reduced to a safe level, and the purging operation can be stopped at this point. However, considering that when the gas concentration at the gasification channel outlet drops to a safe level, there is a possibility that the gas concentration may rebound due to instability, stopping the purging operation too early will cause gas to re-accumulate. Judging by a single concentration ignores the risk of rebound, and the gas concentration will rise again, creating a safety hazard.

[0104] Therefore, in the embodiment of the present invention, S43, the criterion for stopping purging is: reading the gas concentration collected at the monitoring position near the gasification channel outlet and analyzing the gas fluctuation rate at each monitoring time.

[0105] When the gas concentration monitored at the monitoring location is less than or equal to the safety standard, the gas fluctuation rate of the previous monitoring time is read, and the gas compensation rate is calculated. The gas fluctuation rate reflects the degree of change in gas concentration, and the gas compensation rate is used to correct the safe gas concentration to prevent the gas concentration from fluctuating upward again to above the safety standard after it has dropped to the safety standard, thus preventing safety hazards.

[0106] The method for calculating the gas fluctuation rate at a certain monitoring time is as follows: calculate the absolute difference between the gas concentration at the current monitoring time and the gas concentration at the previous monitoring time, and use the ratio of the absolute difference to the gas concentration at the previous monitoring time as the gas fluctuation rate at the current monitoring time.

[0107] The gas compensation rate is the average of the gas fluctuation rate over several previous monitoring periods. For example, in this embodiment, the average of the gas fluctuation rate over six previous monitoring periods is used as the gas compensation rate.

[0108] The gas concentration compensation amount is obtained by multiplying the gas safety standard value and the gas compensation rate. The difference between the gas safety standard value and the gas concentration compensation amount is taken as the final safe gas concentration. The gas safety standard value directly uses the upper limit of gas concentration in coal seam working environment specified in the national or industry mandatory safety regulations.

[0109] When the gas concentration at the monitoring location is lower than the final safe gas concentration, the purging process is stopped.

[0110] The judgment and analysis of stopping purging in this invention requires that the gas concentration drop to a safe standard and that it remain stable without rebound over a continuous period of time to avoid accidental shutdown caused by instantaneous achievement of the standard; at the same time, a safety redundancy is reserved through the gas compensation rate to deal with the risk of desorption and rebound of adsorbed gas; and the stability of gas discharge is quantitatively analyzed based on the volatility calculation at multiple monitoring times.

[0111] S50, obtain the operating parameters of the gasification channel, perform a comprehensive score on each sub-region based on the operating parameters, and select the sub-region with the highest score as the ignition point for in-situ underground gasification of the coal seam.

[0112] Considering the significant differences in the local structure of high-gas coal seam gasification channels, their distance from injection points, and geological conditions, which directly affect gas flow distribution, gas mixing efficiency, and combustion stability; using a pre-set ignition point method may lead to gas accumulation in gas flow vortices in areas with excessive curvature at that location; or the inclination angle may deviate from the optimal range, resulting in gasification obstruction or excessively rapid propagation. Therefore, a comprehensive evaluation of the overall score at each location can improve the coal seam gasification effect.

[0113] In an embodiment of the present invention, S51, the parameters considered for comprehensive scoring of each sub-region based on the operating condition parameters include: the curvature of the channel segment where the sub-region is located, the inclination angle relative to the horizontal plane, the distance to the gas injection point, and the geological conditions of the coal seam in the region; the specific analysis method is as follows: read the curvature radius of each sub-region in the ignition area, filter the sub-region with the maximum curvature radius, record the curvature parameter of the sub-region as 1, and the curvature parameter of the remaining sub-regions is the ratio of the curvature radius of the corresponding sub-region to the maximum curvature radius. The larger the curvature radius, the larger the curvature parameter, and the smoother the airflow.

[0114] Read the tilt angle of each sub-region in the ignition area, filter the sub-regions whose tilt angle is within the optimal tilt angle range, and record their tilt parameter as 1. The tilt parameter of the remaining sub-regions is calculated by: calculating the deviation between the tilt angle and the optimal tilt angle range, and taking the difference between 1 and the deviation as the tilt parameter; for example, the optimal tilt angle range is 5°-12°.

[0115] The area within a set distance from the air inlet is defined as the optimal mixing area. The position parameters of each sub-region within the optimal mixing area are recorded as 1, and the position parameters of the remaining sub-regions are determined by the analysis of tilt parameters. For example, the range where the gas is most fully mixed around the injection point is the optimal mixing area in this embodiment, which is the area 25-80 meters away from the injection port.

[0116] A comprehensive score is obtained by analyzing the curvature parameters, tilt parameters, and position parameters of each sub-region.

[0117] In an embodiment of the present invention, the specific analysis method of the ignition point is as follows: the comprehensive score of each sub-region is calculated by linear weighting based on the curvature parameters, tilt parameters and position parameters of each sub-region; and the comprehensive scores of all sub-regions are sorted in descending order, and the sub-region with the highest score is selected as the ignition point for in-situ gasification of coal seam underground.

[0118] For example, in the above comprehensive scoring analysis, the weight of the location parameter is set to 0.4, and the weights of the curvature parameter and the tilt parameter are both set to 0.3. The specific weight settings can also be dynamically adjusted according to the actual geological conditions and gasification process requirements. For example, when the pressure fluctuation of the gas injection system is large, the weight of the location parameter can be appropriately increased to prioritize ensuring sufficient gas mixing; if the overall geological conditions of the coal seam are relatively stable, the weight of the curvature parameter can be increased to ensure smooth flow of gas in the channel and reduce the potential risk of gas accumulation caused by eddies.

[0119] This invention comprehensively determines the ignition point location by taking into account multiple dimensions of data, including the curvature and tilt of the vaporization channel and its distance from the air inlet, thus eliminating any blind spots in the evaluation. This invention adopts a unified quantitative standard, converting all parameters into coefficients in the 0-1 range, which allows for intuitive screening of the final results. Furthermore, by linearly weighting and fusing the parameters, it can adapt to the requirements of gas mixing, combustion propagation, and safe and stable vaporization.

[0120] Once the ignition point is determined, first lower the nozzle of the electric igniter to the ignition point position, and then introduce air and propane gas into the ignition point through the pre-embedded gas injection pipe. Oxygen needs to be added to the air to make the oxygen concentration in the air about 30%.

[0121] When propane and air reach the nozzle, start the electric igniter and observe the nozzle temperature. If the nozzle temperature rises significantly, it indicates that the propane has been ignited.

[0122] Continuing to observe the composition of the outlet gas, the CO2 concentration in the outlet gas continued to rise, CO appeared, the oxygen concentration continued to decrease, and the nozzle temperature continued to rise, indicating that the coal seam was ignited.

[0123] Maintain the ignition status and continue to observe the composition of the outlet gas. The CO2 concentration of the outlet gas continues to rise, and CO, H2, and CH4 appear. The oxygen concentration continues to decrease and is less than 5%. The nozzle temperature continues to rise, indicating that an oxidation zone has formed in the coal seam.

[0124] The gasifier is considered to have been successfully ignited when the nozzle temperature continues to rise, the O2 concentration in the gas at the outlet is close to zero, the calorific value of the gas is greater than 2.5 MJ / Nm3, or the combustible components in the outlet gas are greater than 20%.

[0125] This invention accurately delineates the ignition zone based on data such as the length, width, and coal seam thickness of the gasification channel. Simultaneously, it employs a dual monitoring unit setup for both the ignition zone and the gas transmission direction, achieving blind-spot-free monitoring of the gasification channel. This satisfies the requirements of zoned monitoring while ensuring the continuity and accuracy of parameter acquisition, providing reliable data support for subsequent pressure maintenance, purging, and ignition point selection in the gasification channel. The invention utilizes gas introduction into the gasification channel for pressure maintenance, allowing methane adsorbed in coal seam fissures to precipitate and mix with air, resulting in a more uniform methane distribution throughout the channel and surrounding fissure network. Simultaneously, purging the gasification channel after pressure maintenance ensures rapid methane discharge, improving emission efficiency. The invention introduces dual judgment criteria of average pressure and pressure deviation during pressure maintenance, not only accurately determining a stable pressure maintenance state but also rapidly locating leak points and orifices through pressure residual trend analysis, enabling early sealing to eliminate safety hazards and prevent methane leakage and pressure imbalance caused by leaks.

[0126] This invention constructs a purging performance coefficient using the gas gradient coefficient and the gas pressure influence coefficient, enabling a quantitative evaluation of the purging effect. It can dynamically adjust the airflow to adapt to different purging scenarios and calculates a compensation rate based on the gas fluctuation rate to set the final safe concentration, preventing gas rebound and accumulation after purging and ensuring thorough gas purging. This invention integrates multiple parameters such as channel curvature, inclination, and distance to the injection point, using a linear weighted method to calculate a comprehensive score for sub-regions, accurately selecting the optimal ignition point, ensuring smooth airflow and thorough gas mixing after ignition, and improving combustion stability and gasification efficiency.

[0127] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention, which are still covered within the protection scope of the present invention.

Claims

1. A safe ignition method for underground in-situ gasification of coal in high-gas coal seams, characterized in that, include: Air is injected into the vaporization channel, and pressure holding parameters at each location are obtained through multiple monitoring units installed in the vaporization channel. Based on the pressure holding parameters, determine whether the vaporization channel meets the stable pressure holding state, and perform pressure holding treatment on the gas in the channel if it meets the state. After the pressure holding process is completed, air is introduced into the vaporization channel for purging, and the air pressure and gas concentration at each location are acquired at monitoring times during the purging process. Based on the gas pressure and gas concentration, the purging performance coefficient is analyzed, and the flow rate of the incoming air is adjusted according to the purging performance coefficient until the gas concentration at the air outlet of the vaporization channel drops below the safety standard and purging is stopped. The ignition zone is determined based on the layout parameters of the gasification channel, and the ignition zone is divided into several sub-regions along the coal seam direction. The operating parameters of the gasification channel are obtained, and each sub-region is comprehensively scored based on the operating parameters. The sub-region with the highest score is selected as the ignition point for in-situ underground gasification of the coal seam. The specific analysis method for the purging performance coefficient is as follows: At each monitoring moment, the air pressure and gas concentration at each monitoring location are acquired; Gradient analysis is performed on the gas concentration at each monitoring location and the gas concentration at its adjacent monitoring locations to obtain the gas gradient coefficient at each monitoring location. The average gradient coefficient is then calculated by averaging the gas gradient coefficients. Based on the air pressure analysis of each monitoring location, the air pressure fluctuation values ​​are normalized and converted into an air pressure influence coefficient between 0 and 1. The average air pressure influence coefficient is then obtained by averaging. The average gradient coefficient and the average pressure influence coefficient are linearly weighted to obtain the purging performance coefficient. The criteria for stopping purging are as follows: Read the gas concentration collected at the monitoring location near the gasification channel outlet and analyze the gas fluctuation rate at each monitoring time. When the gas concentration monitored at the monitoring location is less than or equal to the safety standard, the gas fluctuation rate of the previous several monitoring times is read, and the gas compensation rate is calculated. The gas compensation amount is obtained by multiplying the gas safety standard value and the gas compensation rate, and the difference between the gas safety standard value and the gas compensation amount is taken as the final safe gas concentration. When the gas concentration at the monitoring location is lower than the final safe gas concentration, the purging process is stopped.

2. The method for safe ignition of underground in-situ gasification of coal in high-gas coal seams according to claim 1, characterized in that, The monitoring unit is configured as follows: A monitoring unit is set up in each sub-area of ​​the ignition zone; Several monitoring units are evenly arranged along the gas transmission direction of the gasification channel; the monitoring units are used to monitor the pressure holding parameters at the setting location, including gas pressure and gas concentration.

3. The method for safe ignition of underground in-situ gasification of coal in high-gas coal seams according to claim 1, characterized in that, The conditions for determining whether the gas in the vaporization channel undergoes pressure holding treatment are as follows: During the process of injecting air into the vaporization channel, the pressure values ​​at each location are acquired in real time, the average pressure values ​​at each location are calculated, and the pressure deviation at each location is analyzed. For each monitoring location, the absolute deviation between its pressure value and the average value is calculated, and the ratio of the absolute deviation to the average value is taken as the pressure deviation at that monitoring location. Set the pressure holding threshold range and maximum allowable deviation of the vaporization channel; When the average pressure is within the set pressure holding threshold range, and the pressure deviation of all monitoring positions is less than or equal to the maximum allowable deviation, and this continues for a preset duration, the vaporization channel is determined to be in a suitable pressure holding state, and the gas in the vaporization channel is pressure held at the current pressure.

4. The method for safe ignition of underground in-situ gasification of coal in high-gas coal seams according to claim 3, characterized in that, When the pressure deviation at each location exceeds the preset value, it is necessary to analyze the leakage point of the vaporization channel. The specific analysis method is as follows: The pressure residual at each monitoring location is obtained by calculating the difference between the real-time pressure value and the average pressure value of each monitoring unit. All pressure residuals are statistically analyzed, and monitoring locations where the absolute value of the residual exceeds a preset deviation threshold are selected and recorded as pressure anomaly monitoring locations. Read the spatial distribution of the pressure anomaly monitoring location within the vaporization channel. When the pressure residual between adjacent monitoring locations of the pressure anomaly monitoring location shows a continuous increasing or decreasing trend, it is determined that there is a leakage channel in the channel section corresponding to the starting monitoring location to the ending monitoring location of the pressure anomaly monitoring location, and the channel section is recorded as the pressure leakage zone. The pressure leakage area is scanned to determine the specific coordinates of the leakage point and the size of the leakage hole, and then the leakage is sealed with sealing material.

5. The method for safe ignition of underground in-situ gasification of coal in high-gas coal seams according to claim 1, characterized in that, The criteria for determining whether to adjust the airflow rate based on the purging performance coefficient are as follows: If the purging performance coefficient is greater than or equal to the set qualified threshold, the purging effect is judged to be good, and the current airflow is maintained; If the purging performance coefficient is less than the acceptable threshold, the airflow rate needs to be increased.

6. The method for safe ignition of underground in-situ gasification of coal in high-gas coal seams according to claim 1, characterized in that, The specific analysis method for the ignition zone is as follows: Obtain parameters such as the directional length, channel width, and coal seam thickness of the gasification channel; The midpoint of the stated directional length is taken as the end boundary of the ignition region; Starting from the air inlet of the gasification channel, a predetermined safe distance is extended inward along the direction of the gasification channel, and the end point of the extension is taken as the starting boundary of the ignition area; wherein, the safe distance is determined based on the channel width and the coal seam thickness. The vaporization channel section between the starting boundary and the ending boundary is designated as the ignition zone.

7. The method for safe ignition of underground in-situ gasification of coal in high-gas coal seams according to claim 1, characterized in that, The parameters considered in the comprehensive scoring of each sub-region based on the aforementioned operating parameters include: the curvature of the channel segment where the sub-region is located, the dip angle relative to the horizontal plane, the distance to the gas injection point, and the geological conditions of the coal seam in that region; the specific analysis method is as follows: Read the curvature radius of each sub-region in the ignition area, filter the sub-region with the maximum curvature radius, and record the curvature parameter of the sub-region as 1. The curvature parameter of the remaining sub-regions is the ratio of the curvature radius of the corresponding sub-region to the maximum curvature radius. Read the tilt of each sub-region in the ignition area, filter the sub-regions whose tilt is within the optimal tilt range, and record their tilt parameter as 1. The tilt parameter of the remaining sub-regions is calculated by: calculating the deviation between the tilt and the optimal tilt range, and using the difference between 1 and the deviation as the tilt parameter. The area within the set range of the air inlet is defined as the optimal mixing area. The position parameters of each sub-region located in the optimal mixing area are recorded as 1, and the position parameters of the remaining sub-regions are determined by the analysis of the tilt parameters. A comprehensive score is obtained by analyzing the curvature parameters, tilt parameters, and position parameters of each sub-region.

8. The method for safe ignition of underground in-situ gasification of coal in high-gas coal seams according to claim 7, characterized in that, The specific analysis method for the ignition point is as follows: The comprehensive score of each sub-region is calculated by linear weighting based on the curvature, tilt and location parameters of each sub-region. The comprehensive scores of all sub-regions are then sorted in descending order, and the sub-region with the highest score is selected as the ignition point for in-situ underground gasification of the coal seam.

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