A method for predicting the hydrogen sulfide hazard of coal seams

Abstract

This invention relates to the field of coal mine safety, specifically to a method for predicting the risk of hydrogen sulfide outbursts in coal seams. Currently, manual sampling for hydrogen sulfide gas detection in domestic mines is highly dangerous; furthermore, dissolved hydrogen sulfide is corrosive to mechanical measuring devices, resulting in low efficiency and the need for corrosion protection. This invention first determines the presence of geological water in the coal seam. If geological water is present, a small amount is deacidified and then tested with lead acetate test paper. If no geological water is present, a safe pH range is determined through mathematical statistics. While drilling into the coal seam at the measurement location in the tunneling face or return airway, the borehole flushing fluid is recovered, the pH value is measured, and the average value is calculated and compared with the safe pH range to determine whether there is a risk of hydrogen sulfide outbursts in the coal seam. This invention is highly practical in underground operations, highly safe, simple to operate, low in cost, and provides rapid and timely results, effectively ensuring the safety of underground workers and the safe and efficient production of coal mines.

Description

Technical Field

[0001] This invention relates to the field of coal mine safety, and in particular to a method for predicting the hydrogen sulfide hazard in coal seams in advance. Background Technology

[0002] As shallow-buried mines close and mining gradually shifts towards deeper mines, coal seam geological conditions become increasingly complex. Mining efforts are shifting from easily minable, low-sulfur, stable coal seams to difficult-to-mine, high-sulfur special coal seams, thus increasing the likelihood of hydrogen sulfide gas outbursts. Hydrogen sulfide, a colorless, highly toxic gas with a rotten egg smell, is extremely harmful to human health. At a volume fraction of 0.002%, symptoms include headaches and pulmonary edema; at 0.01%, coughing and difficulty breathing occur; and at 0.1%, loss of taste and brain death result. Furthermore, hydrogen sulfide is readily soluble in water, forming acidic solutions that corrode underground machinery, causing damage and impacting mine production.

[0003] Currently, my country mainly determines the hydrogen sulfide gas content in coal seams through the development of measuring devices and laboratory gas analysis. However, this method is difficult to implement, inefficient, and the hydrogen sulfide gas is corrosive to the measuring devices, requiring corrosion resistance and increasing costs. Therefore, there is an urgent need for a simple and quick method suitable for the underground working environment of coal mines to preliminarily determine whether a mine has a hydrogen sulfide outburst. Summary of the Invention

[0004] The purpose of this invention is to develop a novel method for predicting the danger of hydrogen sulfide in coal seams in advance. Based on the test results, timely measures can be taken to prevent hydrogen sulfide outburst accidents and avoid casualties.

[0005] This method is low-cost, requires no special equipment, and has a simple operation procedure that does not require professional training. Furthermore, it offers a degree of timeliness, allowing for the implementation of appropriate protective measures based on test results within a short period, thus preventing accidents and injuries. Although low-cost, its underlying principle is reliable; the formula is as follows:

[0006] SO4 2- +2C + 2H₂O = 2HCO₃ - +H2S↑ ①

[0007] H2S=H + +HS - HS - =H + +S 2- ②

[0008] Coal seams contain a large amount of adsorbed and free hydrogen sulfide gas. One mechanism is due to the occurrence of reaction ①, which decreases the concentration of sulfate ions and increases the concentration of bicarbonate ions and the content of hydrogen sulfide gas in the coal seam, leading to an increase in the HCO3 content in the drilling fluid of the coal seam. - SO4 2- The ion concentration ratio will be much higher than in normal mines, which will lead to a decrease in the pH value of the borehole flushing fluid.

[0009] Secondly, hydrogen sulfide gas is readily soluble in water. When hydrogen sulfide gas in the coal seam encounters the borehole flushing fluid, it dissolves in the fluid, leading to reaction ②. Hydrogen sulfide gas dissolves in water to form a hydrosulfuric acid solution. Hydrosulfuric acid is a diprotic weak acid, and it ionizes to release a large number of hydrogen ions, thus lowering the pH value of the borehole flushing fluid.

[0010] In summary, the aforementioned two reactions cause a decrease in the pH value of the borehole flushing fluid, making it weakly acidic and below the safe range. With the pH value within the safe range, the hydrogen sulfide gas in the coal seam is at a normal level, or even poses no risk of hydrogen sulfide outburst. Therefore, no special measures are needed to prevent hydrogen sulfide outbursts. Furthermore, since the drill pipe length is controllable, when the drill pipe reaches the predicted coal seam location, the borehole flushing fluid at that location can be recovered. By measuring the pH value of this flushing fluid, the hydrogen sulfide gas level at the corresponding location in the coal seam can be determined. Attached image description:

[0011] Figure 1 This is a process flow diagram of the present invention;

[0012] Figure 2 This is a construction diagram of the present invention;

[0013] Figure 3 This is a schematic diagram of the recycling device of the present invention; Detailed implementation method:

[0014] The present invention will be further described below with reference to the accompanying drawings and specific examples.

[0015] Example 1:

[0016] A method for predicting the hydrogen sulfide hazard of coal seams, such as Figure 1 , 2 As shown in Figure 3, proceed with the following steps.

[0017] (1) Use interval estimation to determine the confidence interval for pH value

[0018] ① Data Acquisition

[0019] In adjacent coal seams within the same mining area, where no hydrogen sulfide outburst hazard is known, boreholes are drilled at different locations. For the same borehole, the flushing fluid is rinsed with clean water and recovered. The flushing fluid is shaken well, and the contact head of a pH meter is immersed in the recovered fluid. The pH values ​​are measured and recorded multiple times, with the average value for the same borehole taken and rounded to two decimal places. The pH values ​​of the flushing fluids are measured multiple times in different boreholes. The average pH value measured in the same borehole, rounded to two decimal places, is denoted as x1. The average pH values ​​measured in other boreholes are then x2, x3, x4, x5…x n .

[0020] ② Parameter Calculation

[0021] The measured pH values ​​X~N(μ,σ) 2 Interval estimation is used to define the confidence interval for the pH value. This practical problem is based on the premise that μ is known and σ is... 2 In the unknown normal distribution mathematical model, since pH is greater than 7, meaning the coal seam is in an alkaline environment with no large amount of hydrogen sulfide present, the safe range for this pH value is (K, 14). The value of K in this model is equivalent to finding the one-sided confidence interval of μ with a confidence level of 1-α. The method for determining the value of K is as follows:

[0022]

[0023] Since the upper limit of the safety margin is 14, we only consider the lower confidence bound. Therefore, we require:

[0024]

[0025] According to the definition of the quantile of the t-distribution, we know that k = t 1-α (n-1). Simplifying the inequality within the curly braces in (2), we get:

[0026]

[0027] The one-sided confidence interval for μ at a confidence level of 1-α is: but

[0028]

[0029]

[0030]

[0031] The measured data are x1, x2, x3, x4, x5...x n Substituting into formulas (4), (5), and (6), we get... S * .

[0032] Definition of a statistic:

[0033] Sample mean;

[0034] S *2 Correcting the sample variance;

[0035] S * Correct the sample mean square error;

[0036] μ; population mean;

[0037] σ 2 Overall variance;

[0038] n, sample size;

[0039] N, total size;

[0040] ③ Determining the confidence interval: Based on the above, the lower limit of the one-sided confidence interval for μ with a confidence level of 1-α is... in S * Based on the previous step, t can be obtained. 1-α (n-1) can be found in the t-distribution quantile table.

[0041] Table 1. Quantiles of the t-distribution (P{t≤t) α (n)}=α)

[0042]

[0043]

[0044] If n > 45, it is generally not possible to directly find the quantile table of the t-distribution. In this case, the approximate formula (7) is used.

[0045] t α (n)≈u α (7)

[0046] Table 2 Standard Normal Distribution Table

[0047]

[0048] ④ Values ​​of α

[0049] α is called the significance level, and 1-α is called the confidence level. The smaller α is, the lower the probability of error, the longer the confidence interval, but the lower the estimation accuracy. Conversely, the larger α is, the higher the risk of misjudgment, but the higher the estimation accuracy. Therefore, the value of α should be chosen reasonably according to the actual situation to ensure good accuracy while maintaining a low probability of error. Considering that pH measurement requires appropriate accuracy but the probability of error should be as low as possible, α can be selected as 0.025 or 0.05.

[0050] If the accuracy requirement is relatively small, but the confidence level requirement is relatively high, then α is selected as 0.025.

[0051] If the accuracy requirement is relatively high, while the confidence requirement is relatively low, then α is selected as 0.05.

[0052] (2) Determine the location of the coal seam to be measured

[0053] To conduct preliminary hydrogen sulfide gas level measurements in a coal seam, several considerations are involved during coal seam mining. First, the hydrogen sulfide content varies across different coal seams, necessitating the determination of a specific seam for measurement. Second, hydrogen sulfide is not uniformly distributed within the same coal seam; areas with special geological structures are more likely to experience hydrogen sulfide outbursts, and the seams tend to extend further along their dip and strike directions. Therefore, the first step is to determine the coal seam stratum to be measured and its measurement location. To determine the measurement location for a specific coal seam, the seam is first located along the advancing direction. Then, using the direction perpendicular to the advancing direction as the reference, the seam is divided into several segments, with each segment representing a single drill pipe section, to determine the measurement location.

[0054] Of course, if it is necessary to understand the hydrogen sulfide level of each coal seam, the pH of the borehole flushing fluid in all seams can be measured. Similarly, if it is necessary to understand the hydrogen sulfide level in different areas of the same coal seam, the pH of the recovered borehole flushing fluid in all areas of the coal seam can be measured segment by segment. If the hydrogen sulfide level in a certain segment is high, advanced hydrogen sulfide control measures can be implemented in that segment of the coal seam to prevent accidents such as casualties when mining back to that location.

[0055] (3) Hydrological exploration and geological water treatment

[0056] Hydrological surveys are conducted at the measurement location. If geological water is present at the location, a small amount of the geological water is taken for testing with test strips. The geological water should first be deacidified, as the concentration of sulfate ions in coal seams is much higher than that of sulfide ions. To prevent the sulfate ions in the geological water from reacting with the lead ions in the test strip to form a white lead sulfate precipitate, which would affect the color reaction of the test strip and also compete with the lead ions in the test strip, an appropriate amount of barium chloride solution is added to the geological water. After sufficient reaction, the sulfate ions are removed. Then, the clear upper layer of the solution is taken for test strip testing. If the test strip turns black, hydrogen sulfide treatment is required. If the test strip does not change color or turns light yellow, minimal pretreatment is not necessary.

[0057] The reaction principle of lead acetate test paper: Pb(CH3COO)2 + H2S = PbS↓ + 2CH3COOH

[0058] Deacidification principle: BaCl2 + SO4 2- =BaSO4↓+2Cl -

[0059] If the measurement location does not contain geological water, proceed with steps (4), (5), (6), (7) and (8) in sequence.

[0060] (4) Determine the drill pipe length and number of sections

[0061] Once the location of the coal seam to be measured is determined, i.e., the distance from the coal face to the measurement location is known, the number of drill pipe sections is determined accordingly, since the length of a single drill pipe section is fixed. The coal seam is divided into several segments, perpendicular to the drilling direction, using the length of a single drill pipe section as the unit. The number of drill pipe sections to reach the predicted measurement location is marked. When the measurement area is far from the drilling rig, multiple drill pipe sections are used as one segment length; when the measurement area is close to the drilling rig, a single drill pipe section is used as one segment length. This ensures that the drill pipe accurately reaches the predicted location.

[0062] (5) Drill to the measurement position

[0063] Based on the determined coal seam location, drilling is carried out in the return airway at a 1° elevation angle to facilitate drainage until the marked drill rod is connected to the drilling rig and enters the coal seam, at which point the drill rod reaches the predicted position. After the drill rod reaches the predicted position, it is necessary to briefly maintain the drill rod's rotation in place until the final section is drilled to ensure that the drilling flushing fluid fully contacts the coal seam and is smoothly discharged.

[0064] (6) Recovering borehole flushing fluid

[0065] The drilling flushing fluid is sprayed from the nozzle and travels along the drill rod into the borehole. On one hand, the flushing fluid cools the drill rod to prevent burnt-out; on the other hand, it hydraulically removes slag to prevent borehole blockage. The flushing fluid is simply clean water, which is low-cost and readily available. When the marked drill rod is connected to the drilling rig and drilling begins, a recovery device is installed. A recovery tank is placed at the bottom of the drill rod to collect the drilling flushing fluid. The tank opening has a 5mm diameter filter to prevent small-diameter coal particles from entering the recovery unit. Simultaneously, the head end of the diversion plate is inserted into the coal wall, and the bottom anti-slip buckle of the diversion plate rests against the edge of the recovery tank. A diversion hose connects the end of the drilling rig to the end of the diversion plate. Once the recovery device is installed, [further details are needed]. Figure 3 As shown. Flushing fluid is collected from the start of the marked drill rod contacting the coal face until the end of the last segment at the measurement location. When drilling to the end, the drill rod is rotated in place for 1 minute, and the borehole flushing fluid in the measurement area is completely recovered.

[0066] (7) pH meter to measure the rinsing solution

[0067] After recovering the borehole flushing fluid, shake the fluid well, open the filter, place the pH meter contact head into the recovery unit, measure and record the pH value, keeping two decimal places. Take the average of multiple pH measurements of the borehole flushing fluid, shaking the fluid in the recovery unit well before each measurement.

[0068] (8) Determine if there is a risk of hydrogen sulfide flare.

[0069] If the pH value is within the reference range, the flushing fluid is neutral or even alkaline, and there is almost no risk of hydrogen sulfide gas outburst in the coal seam testing area. If the pH value is not within this defined range, the flushing fluid is weakly acidic or acidic, and the hydrogen sulfide level in the coal seam testing area is high, making it easy for hydrogen sulfide outburst accidents to occur when mining in this area.

Claims

1. A method for advance prediction of hydrogen sulfide hazard in coal seams, characterized by, The method comprises the following steps: (1) The interval estimation is used to determine the pH value confidence interval; the drillings of different positions are carried out in the arbitrary coal seam of the adjacent mine in the same minefield which is known to have no hydrogen sulfide outburst danger; the drillings are washed with clean water and the washing liquid is recovered; the contact head of the pH meter is put into the washing liquid, the pH value is measured for many times and the value is recorded; the average value of the same drilling is taken, different drillings are measured for many times, and the pH value of the washing liquid is recorded; the measured pH value X~N(μ,σ 2 ) is used to determine the pH value confidence interval by the interval estimation; the safe range of the pH value is (K, 14), the value K is the one-sided confidence interval of the confidence level of 1-α on the normal distribution mathematical model; the one-sided confidence interval of the confidence level of 1-α of the solved μ is , then ; wherein, is the sample mean, is the corrected sample mean square deviation, n is the sample size, 1-α is the confidence level, is obtained according to the t distribution quantile table; (2) determining the position of the coal seam; performing preliminary hydrogen sulfide gas level determination on a certain coal seam, and performing pH determination on drilling flushing fluid of the coal seam at all horizons; if the hydrogen sulfide levels of each region of the coal seam at the same horizon are to be known, the drilling flushing fluid recovered from all regions of the coal seam is subjected to regional pH determination in sections; if the hydrogen sulfide level of a certain section is high, the coal seam in the section is subjected to advanced hydrogen sulfide treatment; when the position of a certain coal seam is determined, the certain coal seam is first positioned according to the advancing direction, then divided into sections with a single drill rod length as a unit in a direction perpendicular to the advancing direction, and the position is determined; (3) hydrological detection and geological water treatment; the position is subjected to hydrological detection, and if the position contains geological water, a small amount of the geological water is subjected to test paper detection; the geological water is subjected to deacidification treatment, barium chloride solution is added to the geological water, the solution is fully reacted and then the sulfate in the solution is removed, and then the upper clear liquid of the solution is subjected to test paper detection; if the test paper turns black, advanced hydrogen sulfide treatment is needed, and if the test paper does not change color or is light yellow, excessive advanced treatment is not needed; if the position does not contain geological water, steps (4), (5), (6), (7) and (8) are sequentially performed; (4) determining the length of the drill rod and the number of sections; the coal seam is divided into sections with a single length of the drill rod as a unit, and the number of sections of the drill rod reaching the position is marked; (5) drilling to the position; drilling is performed at an angle of 1° in the return airway according to the determined position of the coal seam; (6) recovering the drilling flushing fluid; the flushing fluid is collected from the time when the marked drill rod contacts the coal wall to the time when the drilling reaches the last section of the position, and the drilling flushing fluid in the region is recovered after the drill rod is kept rotating in place for 1 minute; (7) determining the flushing fluid by a pH meter; (8) determining whether there is a hydrogen sulfide outburst risk; if the pH value is within the reference range, the flushing fluid is neutral or alkaline, and the coal seam determination region does not have a hydrogen sulfide outburst risk; if the pH value is not within the reference range, the flushing fluid is weakly acidic or acidic, and the coal seam determination region has a high hydrogen sulfide level and is prone to a hydrogen sulfide outburst risk during mining.

2. The method of claim 1, wherein, The pH value of the drilling flushing fluid recovered by advanced determination is used to determine the hydrogen sulfide level of the coal seam.

3. The method of claim 1, wherein, The pH value reference range is determined by determining and analyzing a large amount of pH data of adjacent mines under the same ore-forming conditions, and the pH value reference range can be repeatedly used in adjacent mines and continuously improved in accuracy by using data.

4. The method of claim 1, wherein, Based on the lead acetate test paper reaction principle and combined with the actual conditions underground, deacidification treatment is performed to avoid affecting the test paper comparison.

5. The method of claim 1, wherein, The flushing fluid is recovered by a drilling flushing fluid recovery device, which has a simple structure, low cost and is easy to operate.

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