Coal field fire area air pollutant emission amount accounting method and governance emission reduction amount accounting method

Abstract

The invention discloses a coal field fire area air pollutant emission amount accounting method and a governance emission reduction amount accounting method, and relates to the technical field of environmental science, the coal field fire area air pollutant emission amount accounting method comprises the following steps: obtaining coal field fire area basic information, and combining pollutant emission factors to determine source intensity; and acquiring coal field geological channel information, determining a migration transformation coefficient, a release coefficient, a migration coefficient synergistic factor and a release coefficient synergistic factor, and further calculating the coal field fire area atmospheric pollutant emission. By quantifying the synergistic effect of the'source intensity 'and the'geological path', differentiated and refined evaluation of coal field fire area pollutant emission under different geological conditions is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of environmental science and technology, in particular to a coalfield fire area atmospheric pollutant emission accounting method and a treatment and emission reduction accounting method. BACKGROUND

[0002] The severity of coalfield fires is due to the dual effects of natural and human factors: on the natural level, crustal movement exposes deep coal seams to the surface, and in arid and dry, strongly dissected topographic environments, coal seams are easily ignited after contacting oxygen due to their own characteristics; on the human level, the disorderly mining of small coal mines in history has led to the closure of goaf, and the destruction of the surface cover layer by random digging has exposed deep coal seams that were originally isolated from air, and through oxidation reaction, heat is accumulated to form a large-scale fire area.

[0003] The continuous combustion of coalfield fires has caused major environmental disasters, not only causing surface subsidence, vegetation extinction and soil acidification, forming a continuous "ecological desert", but also continuously consuming valuable coal resources. Coal seam oxidation combustion not only releases a large amount of heat energy, but also produces various harmful substances and particulate matter, mainly including greenhouse gases (such as CO2, CH4, N2O), toxic gases (such as CO, SO2, H2S, NOx), incomplete combustion organic compounds and suspended particulate matter / aerosol. These emissions are an important reason for aggravating global climate warming, air pollution, and phenomena such as haze and acid rain. At the same time, the underground cavities formed by the burning of coal seriously damage the geological structure, induce potential geological disasters such as surface subsidence, ground cracking and large-scale subsidence, seriously threaten the safety production of coal mines, and cause direct or indirect huge social and economic losses.

[0004] Under this background, it is of urgent practical significance to build a precise accounting technology system for pollutants in coalfield fire area treatment: on the one hand, it can provide dynamic quantitative management basis for fire extinguishing engineering, optimize the treatment strategy of grouting, stripping and other strategies in real time, and improve the treatment efficiency and accuracy; on the other hand, the atmospheric pollutant emission reduction formed by the treatment of coalfield fire area can be used as a source of total atmospheric pollutant replacement index for new projects in the region, effectively breaking the bottleneck faced by new projects due to insufficient replacement sources of regional reduction, and providing strong support for industrial development.

[0005] Currently, there are two technical bottlenecks in the evaluation of coalfield fire area pollutant emissions: 1. Insufficient evaluation accuracy: traditional methods simply apply domestic coal emission factors, and fail to fully consider the fundamental influence of the unique oxygen-poor / oxygen-rich environment of underground combustion in coalfield fires on pollutant generation mechanism.

[0006] 2. The model is too simplified: existing models usually regard the fire area as a homogeneous "black box", ignoring the key control effect of geological paths (such as fire source depth, cover layer characteristics, fracture development degree, and release mode) on the actual emission of pollutants in the complex process of pollutant migration from the underground combustion source to the surface release. This leads to a large deviation between the accounting results and the actual situation, and cannot provide reliable basis for accurate countermeasures of treatment engineering and scientific evaluation of emission reduction benefit. SUMMARY

[0007] In view of the above problems in the prior art, the coal fire area atmospheric pollutant emission accounting method and the treatment and emission reduction accounting method provided by the present application solve the problem of large deviation between the accounting results of the coal fire area atmospheric pollutant emission and the actual situation in the prior art.

[0008] In order to achieve the above-mentioned purposes, the technical scheme adopted by the present application is as follows: The present application provides a coal fire area atmospheric pollutant emission accounting method, which comprises the following steps: Obtain the basic information of the coal fire area, combine the pollutant emission factor, and then determine the source strength; Obtain the geological channel information of the coal field, determine the migration and transformation coefficient, the release coefficient, the migration coefficient synergistic factor and the release coefficient synergistic factor; Calculate the coal fire area atmospheric pollutant emission according to the source strength, the migration and transformation coefficient, the release coefficient, the migration coefficient synergistic factor and the release coefficient synergistic factor; The migration and transformation efficiency represents the loss rate of pollutants migrating from the combustion area to the ground surface; the release coefficient represents the proportion of pollutants released through the emission port; the migration coefficient synergistic factor represents the influence of the coupling effect between the fire source depth and the cover layer type on the migration and transformation coefficient; and the release coefficient synergistic factor represents the influence of the coupling effect between the fracture development degree and the pollutant release mode on the release coefficient.

[0009] The present application provides a treatment and emission reduction accounting method based on the coal fire area atmospheric pollutant emission accounting method, which comprises: Obtain the coal fire area atmospheric pollutant emission before and after treatment by using the coal fire area atmospheric pollutant emission accounting method, and then obtain the treatment and emission reduction; The coal fire area atmospheric pollutant emission after treatment is obtained by field data collection and calculation after the completion of the treatment construction, or by mathematical modeling to estimate the coal fire area basic information and the coal field geological channel information after the completion of the treatment construction.

[0010] The present application has the advantages that the synergistic effect of "source strength" and "geological path" is quantified, and the differentiated and refined evaluation of the pollutant emission of the coal fire area under different geological conditions is realized. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 A flowchart of the coalfield fire area atmospheric pollutant emission accounting method; Figure 2 An analytical model of underground coal seam combustion pollutant gas seepage constructed for the embodiment; Figure 3 Pollutant gas emission time curves for different fire source depths; Figure 4 Pollutant gas emission time curves for different rock fracture degrees; Figure 5 Pollutant gas emission time curves for different overburden types; Figure 6 Pollutant gas emission time curves for different overburden thicknesses; Figure 7 Pollutant gas emission time curves for different emission port types. DETAILED DESCRIPTION

[0012] The specific embodiments of the present application are described below to facilitate the understanding of the present application for those skilled in the art, but it should be clear that the present application is not limited to the scope of the specific embodiments, and for those skilled in the art, it is obvious that various changes are within the spirit and scope of the present application as defined and determined by the appended claims, and all applications utilizing the concept of the present application are within the scope of protection.

[0013] As shown in Figure 1 The coalfield fire area atmospheric pollutant emission accounting method includes the following steps: S1, obtaining coalfield fire area basic information, combining pollutant emission factors to determine source strength; S2, obtaining coalfield geological channel information to determine migration and transformation coefficients, release coefficients, migration coefficient synergistic factors and release coefficient synergistic factors; S3, calculating the coalfield fire area atmospheric pollutant emission according to the source strength, migration and transformation coefficients, release coefficients, migration coefficient synergistic factors and release coefficient synergistic factors; Among them, the migration and transformation efficiency represents the loss rate of pollutants migrating from the combustion zone to the ground surface; the release coefficient represents the proportion of pollutants released through the emission port; the migration coefficient synergistic factor represents the influence of the coupling effect between the fire source depth and the overburden type on the migration and transformation coefficient; the release coefficient synergistic factor represents the influence of the coupling effect between the fracture development degree and the pollutant release mode on the release coefficient.

[0014] The management and emission reduction amount accounting method based on the coalfield fire area atmospheric pollutant emission accounting method includes: The atmospheric pollutant emission amount of the coalfield fire area before and after treatment is obtained by using the coalfield fire area atmospheric pollutant emission amount accounting method, and then the treatment emission reduction amount is obtained. Among them, the atmospheric pollutant emission amount of the coalfield fire area after treatment is collected and calculated on site after the completion of the treatment construction, or the basic information of the coalfield fire area and the coalfield geological channel information after the completion of the treatment construction are estimated by mathematical modeling and calculated.

[0015] In this embodiment, for the range and depth of the fire area, space-ground-hole integrated detection and sensing technology can be used to identify the macroscopic fire source area and hidden fire source point of the coalfield fire area, and the positioning accuracy of the fire area boundary can be realized to be 5 meters, and the detection rate of hidden fire sources is more than 90%. The main technical means are: remote sensing thermal anomaly monitoring (satellite / unmanned aerial vehicle thermal infrared) + ground geophysical exploration (temperature measurement drilling, resistivity method, magnetic method) + geological modeling, and then the three-dimensional spatial distribution, area and volume of the combustion area are estimated.

[0016] For the coal quality characteristics, this embodiment can collect samples of adjacent unburned coal seams or combustion residues for laboratory analysis to obtain the sulfur content (S%), ash content (A%), volatile matter (V%), fixed carbon (FC%), calorific value, elemental analysis (C, H, O, N, S), etc.

[0017] For the combustion state, this embodiment can perform surface gas composition monitoring (CO / CO2 ratio, CH4 concentration), thermal infrared temperature inversion (distinguish between open fire and smoldering), drilling temperature profile, etc. to obtain the combustion temperature range, main combustion type (open fire / smoldering), and oxidation state (oxygen-rich / oxygen-poor).

[0018] Through the above analysis of the basic information of the fire area, the area of the fire area, the type of coal seam, the average thickness of the coal seam, the density of the coal, and the combustion type are obtained, and the annual loss of coal in the coalfield fire area can be calculated.

[0019] For the geological path, this embodiment can perform geological mapping, fracture investigation, drilling core analysis (overburden lithology, thickness, permeability), and obtain groundwater data to establish a conceptual / numerical model (such as TOUGH2, COMSOL) to simulate the migration path of pollutants from the combustion area to the surface, and estimate the loss rate (1-η2) caused by adsorption, dissolution, and chemical reaction. The overburden is thick and dense (such as clay): η2 is low; fracture development: η2 is high and the release coefficient R is concentrated.

[0020] For the positioning and characterization of the emission port, this embodiment can use unmanned aerial vehicle infrared / visible light aerial photography, ground reconnaissance, and gas concentration walking scanning to identify the location, type (point source / surface source), and relative intensity of the main emission port. Estimate the release coefficient R of different emission ports or areas. Concentrated emission points: R≈1; diffuse emission area: R needs to estimate the area ratio and flux density.

[0021] Through the geological channel information evaluation, the fire source depth of the coalfield fire area, the coal seam fissure degree, the type and thickness of the overburden layer, and the discharge port type are obtained, and then the migration and conversion efficiency η2 and the release coefficient R can be determined.

[0022] The space-air-ground hole collaborative integrated detection and sensing technology is adopted to identify the macroscopic fire source area and the hidden fire source point of the coalfield fire area, to provide data basis for the calculation of the fire area characteristic "source" strength, and to test the fire area treatment effect. The technology can achieve 5-meter positioning accuracy of the fire area boundary and the hidden fire source detection rate is over 90%. The main technical means are as follows: Multi-source remote sensing: using Sar image, multi-spectral, thermal infrared, night light, etc. to invert the ground temperature field, identify the fire area and boundary; Unmanned aerial vehicle survey: equipped with visible light and thermal infrared dual-mode sensor to build a three-dimensional model of the fire area; use time-lapse aeromagnetic technology to identify the burned and altered rock area (high magnetic susceptibility) and the fire area; Ground and underground monitoring: using borehole temperature sensing network and real-time gas component analysis to identify underground hidden fire sources.

[0023] The three-dimensional monitoring network is constructed by using remote sensing + fixed-point monitoring technology to monitor and identify the pollutant emissions before and after the treatment of the coalfield fire area, to provide testing for the fire area treatment effect, and to provide verification for the pollutant emission accurate calculation model. The main technical means are as follows: Horizontal remote sensing: using differential optical absorption spectroscopy (DOAS) to draw a hundred-meter resolution distribution map to obtain the 360-degree horizontal spatial distribution of pollutants and locate the high emission area; Vertical remote sensing: using LiDAR to obtain the 0~4km height distribution of pollutants to obtain the high-altitude transmission rule; High-altitude super-optical imaging: online monitoring of emission.

[0024] In this embodiment, the annual loss of coal quantity multiplied by the pollutant emission factor is used to evaluate the atmospheric pollutant emission source strength of the coalfield fire area: Source strength (E) = Annual loss of coal quantity (M) × Pollutant emission factor (EF) Wherein: Source strength (E): the annual total emission amount of the target pollutant (such as particulate matter, sulfur dioxide, nitrogen oxide, volatile organic compounds, etc.); Annual loss of coal quantity (M): the total amount of coal consumed by the coalfield fire area in a year due to combustion; Pollutant emission factor (EF): the mass of a specific pollutant emitted per unit mass of coal combustion.

[0025] In the specific implementation process, the existing indirect measurement method calculates the emission, and the main principle is to measure the ground surface temperature and area of the fire area, calculate the heat emitted by the coalfield fire area per year, and then calculate the annual coal consumption of the fire area through heat balance calculation.

[0026] The annual coal consumption of the coalfield fire area is determined by the temperature field method: first, the temperature grid measurement of the abnormal temperature area of the ground surface of the fire area is performed; second, the temperature contour map is drawn by using the collected coordinates and temperature data, and the range area of each temperature interval is counted; then, according to the heat dissipation coefficient of different temperature intervals, the heat value released to the atmosphere by each temperature interval per year is calculated and summed up; finally, according to the heat balance theory, the annual loss amount of the fire area is calculated. That is, the loss of coal quantity (M) = heat (Q) / coal combustion value (C).

[0027] Although the above method of measuring and calculating according to the ground surface temperature is relatively accurate, it has certain difficulty in actual operation. Therefore, the embodiment carries out fitting calculation research based on the measured evaluation results of the annual loss of coal quantity, in order to propose a rapid evaluation method of the annual loss of coal quantity. Specifically, according to the fire area, coal quality characteristics, average coal seam thickness, coal density and combustion type, the annual loss of coal quantity of the coalfield fire area is calculated, and the calculation expression is: M fit =α×(A×H×ρ×η1) Among them: Effective combustion area ratio (α): the ratio of the effective combustion area in the fire area to the total fire area. According to regression fitting, α is comprehensively valued according to the combustion type, α=0.18 for open fire, α=0.22 for smoldering, and α=0.2 for open fire+smoldering; Fire area (A): the projection area of the combustion area on the ground surface (m 2 ) is circled through satellite / unmanned aerial vehicle thermal infrared image; Average coal seam thickness (H): the average value of the vertical thickness of the burning coal seam determined by drilling or geophysical prospecting data (m), and the weighted average is taken when there are multiple coal seams; Coal density (ρ): 1.35 tons / m 2 for lignite, 1.45 tons / m 2 for bituminous coal, and 1.55 tons / m 2 for anthracite (preferably measured); Combustion efficiency factor (η1): according to regression fitting, η1=0.85±0.05 (complete combustion) for open fire dominant area, η1=0.65±0.05 (incomplete combustion) for smoldering dominant area, and η1 is calculated according to the area ratio of open fire / smoldering (for example: when open fire accounts for 60%, η1=0.6×0.85+0.4×0.65=0.77).

[0028] According to the "Guidelines for Accounting for Total Emission Reduction of Major Pollutants (2022 Revision)" and related research literature, the burning of domestic coal releases various types of air pollutants, including particulate matter (10-18.8 kg / t), sulfur dioxide (1.5-24 kg / t, depending on the sulfur content of the coal), nitrogen oxides (1.1-3.62 kg / t), and volatile organic compounds (0.18-1.93 kg / t). However, there are differences between coalfield fire combustion and domestic raw coal combustion in terms of pollutant release, such as lower sulfur dioxide emissions from coalfield fire combustion than from domestic raw coal combustion, and higher particulate matter and volatile organic compound emissions from coalfield fire combustion than from domestic raw coal combustion. In addition, the emission factors of particulate matter, sulfur dioxide, nitrogen oxides, and volatile organic compounds released by underground coal fires are highly dependent on the oxygen concentration level (oxygen-rich or oxygen-poor) and the combustion state of the combustion environment. For example, in an oxygen-rich environment, higher oxygen concentrations accelerate combustion reactions, reducing particulate matter and volatile organic compound emissions, but promoting the formation of nitrogen oxides and sulfur dioxide. Conversely, in an oxygen-poor environment, the lack of oxygen creates a reducing atmosphere, leading to incomplete combustion. Under these conditions, particulate matter and volatile organic compound emissions increase, while nitrogen oxide and sulfur dioxide emissions decrease. Taking into account the above factors, the emission factors of the four types of air pollutants from coalfield fires are shown in Table 1.

[0029] Table 1: Emission factors of four types of air pollutants from coalfield fires

[0030] As previously shown, a geological pathway refers to the underground pathway through which pollutants migrate from the fire zone combustion source to the surface or atmospheric environment and its impact effects. In actual coalfield fires, the geological pathway effect is manifested in the influence of factors such as fire source depth, rock fissure degree, overburden type and thickness, and discharge port type on the source strength of the fire zone. Specifically, it can be divided into two categories of factors: one is the migration and transformation coefficient, which represents the loss rate of pollutants migrating from the combustion zone to the surface; the other is the release coefficient, which represents the proportion of pollutants released through the discharge port.

[0031] The migration and transformation coefficient refers to the loss rate of pollutants migrating from the combustion zone to the surface. The geological pathway of atmospheric pollutants from the fire source to the surface is influenced by factors such as fire source depth, rock fissure degree, overburden type and thickness, and is described in detail as follows: (1) Fire source depth The depth of coalfield fire is one of the key factors affecting the type and amount of atmospheric pollutant emissions. This influence is mainly achieved by changing the combustion conditions of the underground coal seam (such as oxygen supply, temperature, pressure, and combustion mode) and the path of pollutant migration to the surface. In terms of oxygen supply and combustion efficiency: shallow fire zones (usually less than 50 meters) are directly affected by surface air convection, with abundant oxygen supply, intense combustion, and high temperature, which promotes the generation of complete combustion products and high-temperature thermal nitrogen oxides, as well as the emission of coarse particulate matter; while deep fire zones (more than 100 meters) gradually turn into anoxic smoldering state due to the exponential rise in oxygen penetration resistance, significantly increasing the proportion of incomplete combustion products. In terms of pollutant migration path and retention: the path of pollutants from the combustion source to the surface in shallow fire zones is usually shorter and more direct (through obvious cracks and collapse pits), with fewer opportunities for oxidation, adsorption, or dilution during migration; deep fire zones require longer and more tortuous cracks, pores, or coal seams to reach the surface, greatly increasing the chances of physical or chemical transformation of pollutants during migration. In addition, the depth of the fire source forms a sharp contrast in surface emission characteristics: shallow fire zones exhibit high-intensity, continuous, and stable point source emissions; deep fire zones show low flux and long duration diffuse emissions, with intermittent and spatially offset release patterns.

[0032] (2) Rock / coal seam fissure degree The rock / coal seam fissure degree has a profound and multi-faceted control effect on coalfield fire pollutant emissions. As an underground channel network, fissures primarily enhance oxygen supply to the fire zone, maintaining and intensifying coal combustion, thereby directly increasing the total amount of combustion and the absolute scale of pollutant generation. Secondly, a highly developed fissure network provides efficient migration channels for various harmful gases and particulate matter generated by combustion, significantly reducing the resistance to pollutant migration to the surface or groundwater, resulting in faster emission rates, increased emission flux, and determining that emission points are mainly concentrated in areas with high fissure development, forming spatially uneven emission "hotspots". At the same time, a favorable fissure system also serves as a path for fire spread to the deep or surrounding areas, indirectly expanding the scope of the pollution source. Therefore, high fissure degree significantly increases pollutant emission volume and intensity, exacerbating environmental hazards by enhancing combustion intensity and providing efficient emission paths.

[0033] (3) Overburden type and thickness The type and thickness of overburden layer above coalfield fire area jointly constitute the key geological barrier to control the release of pollutants to the environment. The type of overburden layer directly determines its resistance to gas migration: low-permeability overburden layer (such as clay, silty clay, etc.) can effectively inhibit the supply of oxygen to the deep fire area, while significantly hindering the upward migration of waste gas produced by combustion, forcing the pollutants to seep through a more tortuous path, thereby greatly reducing the surface emission flux. On the contrary, high-permeability overburden layer (such as sandy soil, blocky gravel soil, etc.) acts as a natural "chimney", providing an unobstructed channel for rapid downward infiltration of oxygen and efficient emission of pollutants, resulting in accelerated emission rate and dispersed emission points.

[0034] The thickness of the overburden layer non-linearly regulates the emission effect by increasing the gas diffusion path length and the degree of heat loss: thin overburden layer has small resistance, and pollutants can easily penetrate quickly, resulting in high surface emission intensity and often associated with high temperature points; overburden layer of medium thickness can prolong the gas migration time, and some pollutants may be degraded during migration due to adsorption, condensation or reaction, but its effect is restricted by lithology and fracture development degree; thick overburden layer has the most significant resistance to oxygen and pollutants, can strongly suppress the surface emission flux, and even make the fire area turn into smoldering state, and the heat of deep waste gas is absorbed by the rock layer during long migration, reducing the temperature. Ultimately, the actual effectiveness of the overburden layer depends on its synergistic effect with the fire source depth, and high-permeability soil coverage produces synergistic effect in deep fire area, while low-permeability soil coverage produces stronger plugging effect in deep fire area. Therefore, the characteristics of the overburden layer deeply affect the emission effect of pollutants.

[0035] According to the above analysis, the migration conversion coefficient η2 value in the embodiment is determined by the fire source depth, the characteristics of the overburden layer, and the fracture development degree. Therefore, the following formula is defined: η2=η0×K 深度 ×K 裂隙 ×K 覆盖层 Wherein η2 is the migration conversion coefficient; η0 is the basic migration coefficient, which is 1.0 by default; K 深度 is the fire source depth correction coefficient; K 裂隙 is the fracture development correction coefficient; K 覆盖层 is the overburden layer type and thickness correction coefficient.

[0036] The values of each coefficient can be determined according to model test research under consideration of each working condition combination. In the embodiment, a conceptual model of underground coal seam combustion is designed as shown in Figure 2The diagram shows a three-dimensional model of pollutant gas seepage from a fire source (gas generation source), a rock layer (including fissures), a soil layer, and an emission outlet. COMSOL software was used to simulate pollutant gas emissions from a coalfield fire zone. The model was scaled to 1:100 and employed a layered structure: a bottom combustion layer (simulating a coal seam), a middle layer of rock fissures, and a top layer of soil cover. The physical field parameters were set as follows: Darcy's law was used to control the gas seepage process in the porous medium, and the rock permeability was set according to the degree of fissure development: 10 for strong fissures. -12 m 2 Medium-sized cracks, 5×10 -13 m 2 Weak cracks 10 -13 m 2 Soil permeability is set according to the type of cover layer: 10 for high permeability type. -12 m 2 Medium osmotic type 5×10 -13 m 2 Low-permeability type 10 -13 m 2 Pollutant migration was simulated using a rare matter transport module, with a diffusion coefficient set to 1×10⁻⁶. -6 m 2 / s. Boundary conditions are set as follows: the bottom vent is set as the mass inflow boundary ( =7×10 -8 kg / (m 2 •s)), the top surface is set as a pressure boundary (p=101325 Pa, simulating atmospheric environment), and all sidewalls and bottom surfaces are set as no-slip walls. The transient solution uses the BDF method, with a time range of 0-100 hours, a step size of 0.1 hours, and a relative tolerance of 0.001.

[0037] Five influencing factors were considered in this experiment: fire source location, rock fissure degree, overburden type, overburden thickness, and discharge outlet type. Based on these factors, different experimental conditions were designed. The fire source depth was controlled by the rock layer thickness, with options for shallow fire sources (15 m), medium fire sources (55 m), and deep fire sources (105 m). The overburden thickness was set in three ways: 5 m, 10 m, and 20 m. The discharge outlet type was set as a point source (5 m diameter circle), a surface source (20 × 20 m square), or a transitional source (annular area). Gas sensors were arranged in two layers within the soil: one at the surface and the other at a central layer 5 m below the surface, with nine sensors in each layer.

[0038] Based on the above simulation scheme and parameter design, the emission patterns of pollutant gases under various influencing factors are described as follows: (1) Depth of fire source like Figure 3As shown, overall, the gas emission concentrations of shallow, intermediate, and deep fire sources all show an increasing trend over time. The gas emission concentration of shallow fire sources is consistently higher than that of intermediate and deep fire sources. This means that shallow fire sources are more susceptible to external factors, leading to faster fire development and a more rapid increase in concentration. For example, within the first 10 hours, the concentration of shallow fire sources reached 1264.9 ppm, while the intermediate and deep concentrations were 1011.9 ppm and 758.9 ppm, respectively. The gas emission concentration of intermediate fire sources falls between that of shallow and deep fire sources. Its upward trend is relatively stable, and while the gap with the shallow fire source concentration widens somewhat over time, it remains relatively stable. The concentration of deep fire sources is the lowest among the three, and its rate of increase is relatively slow. The ratio of the three roughly follows a 1:0.8:0.6 ratio.

[0039] (2) Rock fracture degree like Figure 4 As shown, the gas emission concentrations from strongly, moderately, and weakly developed fractures all exhibit an increasing trend over time. The increase in fracture density is most significant in strongly developed rocks, reaching approximately 4400 ppm after 100 hours; the increase is second most pronounced in moderately developed rocks, reaching approximately 4000 ppm after 100 hours; and the increase in weakly developed rocks is relatively gradual, at approximately 3500 ppm. Overall, the higher the degree of fracture development, the higher the gas emission. The ratio of the three is approximately 1:0.9:0.8.

[0040] (3) Covering layer type like Figure 5 As shown, the gas concentrations of all three permeability types increased over time. The high-permeability type consistently had the highest concentration, followed by the medium-permeability type, with the low-permeability type being the lowest. At 10 hours, the high-permeability type concentration was 1622.6 ppm, the medium-permeability type 1380.3 ppm, and the low-permeability type 1137.0 ppm. By 100 hours, the high-permeability type reached 4920.0 ppm, the medium-permeability type 4290.0 ppm, and the low-permeability type 3660.0 ppm. The ratio of the three roughly followed a 1:0.85:0.7 ratio.

[0041] (4) Covering layer thickness like Figure 6As shown, the gas concentrations corresponding to 5m, 10m, and 20m capping layers all increase with time. The 5m capping layer has the highest gas concentration, followed by the 10m capping layer, and the 20m capping layer has the lowest. For example, after 5 hours, the concentration of the 5m capping layer is 788.82 ppm, the 10m layer is 709.94 ppm, and the 20m layer is 631.06 ppm. By 100 hours, the concentration of the 5m capping layer reaches 5353.25 ppm, the 10m layer is 4818.92 ppm, and the 20m layer is 4284.6 ppm. The ratio of the three roughly follows 1:0.9:0.8, indicating that for every 10 meters increase in capping layer thickness, the release coefficient decreases by approximately 0.9.

[0042] (5) Type of emission outlet like Figure 7 As shown, the point source concentration, transition concentration, and area source concentration all increase over time. The point source concentration is higher than the transition and area source concentrations at most time points, and the transition concentration is higher than the area source concentration. At 5 hours, the point source concentration is 776.31 ppm, the transition concentration is 659.95 ppm, and the area source concentration is 582.47 ppm. By 100 hours, the point source concentration is 4871.92 ppm, the transition concentration is 4143.44 ppm, and the area source concentration is 3659.39 ppm. The ratio of these three concentrations roughly follows a 1:0.85:0.75 ratio.

[0043] Based on the preliminary exploration results of this embodiment, the recommended values ​​for ignition source depth, overburden characteristics, and fissure development coefficient are shown in Table 2.

[0044] Table 2: Values ​​of various influencing parameters of migration conversion coefficient

[0045] The release coefficient refers to the proportion of pollutants released through emission outlets. The release mode of pollutants in coalfield fire areas (whether it is concentrated release from point sources or diffuse release from area sources) has a fundamental impact on the distribution of pollutant environmental concentrations, diffusion patterns, and ecological exposure risks.

[0046] Point source release (e.g., fissure outlets, subsidence pits): When the overlying strata / cover of the fire zone have dominant gas-conducting channels (e.g., faults, intersections of highly connected fissures), pollutants are released at high intensity through a single or a few points, forming a vertical emission stream similar to the "chimney effect." This type of release results in high initial momentum and strong thermal buoyancy of the pollutants, allowing the plume to rise rapidly to higher altitudes near the surface.

[0047] Area source release (e.g. multi-fracture leakage, porous media diffusion): When the overlying strata of a fire zone are highly permeable or contain dense fracture zones, contaminants slowly leak out through a large number of micro-channels, forming a diffuse release zone with a scale of hundreds to thousands of meters. This type of release has a low single-point flux and is prone to persistent accumulation in low-lying areas or under calm wind conditions.

[0048] The release coefficient R value is determined by the characteristics of the release port (point source / area source). According to the preliminary exploration results in the appendix, the preliminary recommended values of the release coefficient are shown in Table 3.

[0049] Table 3: Release coefficient values

[0050] In this embodiment, the correction factors for the migration and release coefficients are determined independently. This method assumes that the effects of each geological factor on the migration and release of pollutants are linearly superimposed and do not interfere with each other. However, there are nonlinear couplings and interactions between key parameters (depth, overburden characteristics, fracture development degree, release mode). For example, depth and overburden: the ground pressure of a deep fire zone can significantly affect the migration speed and efficiency of gas in a highly permeable overburden (such as sandstone), and this effect is not obvious in shallow or low-permeability layers. Fracture and release mode: high-density fractures not only provide channels themselves, but also affect whether the release of pollutants is concentrated point source release or diffuse area source release. The proposal of the synergistic correction factor is to quantify the interaction between these key parameters and solve the problem of insufficient evaluation accuracy of the linear model under complex geological conditions (especially deep, high fracture, and specific overburden combinations).

[0051] In this embodiment, the migration coefficient synergistic factor (Kη) specifically quantifies the effect of the coupling between the depth of the fire source and the type of overburden on the migration and transformation coefficient, as shown in Table 4. The migration coefficient synergistic factor is not a simple depth correction factor or overburden correction factor, but a new effect (promoting or inhibiting migration) that occurs after the combination of the two.

[0052] Table 4: Migration coefficient synergistic factor (depth-overburden) values

[0053] For deep fire zones with high-permeability soil overburden, Kη>1 (1.10), indicating that the pressure generated by the depth and the smooth channels of the high-permeability overburden have a strong synergistic promoting effect, making the actual migration loss smaller (η2 larger) than considering the depth and overburden alone, and the release may be stronger.

[0054] For deep fire zones with low-permeability soil overburden, Kη<<1 (0.70), indicating that the depth pressure cannot effectively overcome the strong resistance of low-permeability clay, and the coupling of the two produces a stronger plugging effect, with a large migration loss (smaller η2), and the release is strongly suppressed.

[0055] For the middle layer fire area covered by high permeability soil, Kη=1.05, which reflects the enhancement effect of thermal convection on migration.

[0056] Release coefficient synergy factor K R The coupling effect between the fracture development degree and the release mode (point source / surface source) of the pollutants is quantified to affect the release coefficient, as shown in Table 5. The core of the release coefficient synergy factor K is to quantify how the development degree of the fracture network amplifies or weakens the release efficiency inherent in a certain release mode.

[0057] Table 5: Release coefficient synergy factor (fracture degree-release mode) value

[0058] Strong fracture combined with surface source release (K R =1.15) is the strongest combination of synergy effect. The surface source release is originally dispersed and inefficient, but the extremely developed fracture network turns the lower part of the entire covering layer into an efficient “screen net” or “capillary network”, so that the pollutants can seep out of the ground quickly and in large quantities through countless small but connected paths, significantly improving the actual release proportion.

[0059] The enhancement effect of strong fracture combined with point source release (K R =1.05) is relatively small, because the point source itself is an advantageous channel, and the high fracture network mainly provides more sufficient “supplement” or stability for the point source.

[0060] Weak fracture has a limiting effect on various release modes (K R <1), because it means that there is not enough channel, which increases the opportunity for the pollutants to be “detained” in the migration path.

[0061] Based on the above source strength quantification and geological path effect evaluation of the atmospheric pollutant release of the fire area, the embodiment proposes the following coalfield fire area atmospheric pollutant emission accounting method: Coalfield fire area atmospheric pollutant emission amount = source strength x migration and conversion coefficient x release coefficient x migration coefficient synergy factor x release coefficient synergy factor.

[0062] In an embodiment of the present application, the coalfield fire area pollutant emission amount evaluation includes coalfield spontaneous combustion period pollutant emission amount accounting, coalfield fire area pollutant emission reduction amount accounting before and after the coalfield fire area treatment, and coalfield fire area pollutant emission reduction amount prediction after the coalfield fire area treatment.

[0063] Coalfield spontaneous combustion period pollutant emission accounting: refers to the total amount of various pollutants actually released into the environment by the fire area in a certain period of time (such as every year, every quarter or the entire spontaneous combustion duration) through scientific methods of measurement, calculation and aggregation. It is the basis data for assessing the degree of environmental hazards of the fire area, developing management programs, setting management goals (emission reduction baseline), and an important input for regional environmental quality assessment and pollutant emission inventory.

[0064] Coalfield fire area pollutant emission reduction accounting before and after management: refers to the total amount of pollutants actually reduced due to management measures by comparing the pollutant emissions of the coalfield fire area before the implementation of the management project (baseline period) and after the completion and stable operation of the management project. It is used to quantitatively assess the actual reduction effect and environmental benefits achieved after the implementation of the management project.

[0065] Coalfield fire area pollutant emission reduction prediction after management: refers to the use of scientific models and methods to estimate the pollutant emission reduction potential or total amount that can be achieved by the management project in the future after complete implementation and achieving the expected effect based on the characteristics of the fire area, management technology scheme, and expected management effect. It is used for feasibility study of management project, pre-evaluation of environmental benefits, optimization of management technology scheme, estimation of atmospheric pollutant emission reduction potential, and support for project funding, etc.

[0066] To verify the accuracy and reliability of the atmospheric pollutant emission accounting method proposed in the present invention, a coalfield fire area in a certain city was selected as a typical case for comparative analysis of field monitoring and model accounting. Through field monitoring of atmospheric pollutant emissions before and after the management of the fire area, the actual emission concentration and flux data of sulfur dioxide (SO2) were obtained, and they were compared with the theoretical emission amount calculated by the method (see Table 6). The comparison shows that the results are highly consistent, verifying the reliability of the accounting method.

[0067] Table 6: SO2 emission verification of a coalfield fire area in a certain city

[0068] In addition, the calculated atmospheric pollutant emissions (SO2: 58,000 tons / year, NOx: 38,000 tons / year) of 84 coalfield fire zones in Xinjiang are highly consistent with the results of the latest satellite remote sensing (TROPOMI / MODIS) inversion estimation of the average annual emissions of various pollutants from coalfield fire zones in Xinjiang from 2018 to 2021 (SO2: 65,000 tons / year, NO2: 31,000 tons / year) by Deng Jinchang et al. (2023), which confirms the reliability of the accounting method (see Table 7 for detailed data comparison). The differences between the results of the two methods may be due to the differences in accounting principles ('bottom-up' model estimation vs 'top-down' remote sensing inversion) and the slight differences in the selection of emission factors for different combustion states. In addition, the study by Deng Jinchang et al. found that the emissions showed a downward trend from 2018 to 2021, which supports the conclusion of the governance and emission reduction benefits calculated in this invention, and together proves the significant environmental positive effect of coalfield fire extinguishing projects.

[0069] Table 7: Xinjiang 84 coalfield fire zone NO x , SO2 emission verification

[0070] In summary, this invention builds the first coalfield fire zone pollutant accounting model that simultaneously couples 'pollution source strength' and 'geological path', first proposes the effective combustion area proportion based on the combustion state (open fire / smoldering) and the differentiated emission factor based on the oxygen environment for coalfield fire zones, and innovatively proposes the coordination correction factor (Kη, K R ), solves the quantification problem of the nonlinear action between geological parameters, greatly improves the accuracy of the accounting under complex geological conditions, and forms a complete technical system from accurate accounting to rapid assessment, which can be directly used to guide fire extinguishing projects, evaluate emission reduction benefits, and support environmental management decisions.

Claims

1. A method for accounting for atmospheric pollutant emissions from a coalfield fire zone, characterized by, The method comprises the following steps: Obtaining the basic information of the coalfield fire area, combining the pollutant emission factor, and then determining the source strength; Obtaining the coalfield geological channel information, determining the migration and transformation coefficient, the release coefficient, the migration coefficient synergistic factor and the release coefficient synergistic factor; Calculating the atmospheric pollutant emission of the coalfield fire area according to the source strength, the migration and transformation coefficient, the release coefficient, the migration coefficient synergistic factor and the release coefficient synergistic factor; Wherein, the migration and transformation efficiency represents the loss rate of the pollutant from the combustion area to the surface; the release coefficient represents the proportion of the pollutant released through the emission port; The migration coefficient synergistic factor represents the influence of the coupling effect between the fire source depth and the cover layer type on the migration and transformation coefficient; the release coefficient synergistic factor represents the influence of the coupling effect between the fracture development degree and the pollutant release mode on the release coefficient.

2. The method according to claim 1, wherein, The specific method for obtaining the basic information of the coalfield fire area comprises: Obtaining the macroscopic fire source area and the hidden fire source point of the coalfield fire area through detection and sensing technology; Collecting the samples of the adjacent unburned coal seam or combustion residues for laboratory analysis to obtain the coal quality characteristics; wherein the coal quality characteristics include the sulfur content, ash content, volatile matter, fixed carbon, calorific value and contained elements of the coal; Obtaining the combustion temperature range, combustion type and oxidation state of the coalfield fire area; wherein the combustion type is open fire or smoldering; the oxidation state is oxygen-rich or oxygen-poor; According to the fire area, the coal quality characteristics, the average coal seam thickness, the coal density and the combustion type, the annual loss of coal quantity of the coalfield fire area is calculated, and the calculation expression is: M fit =α×(A×H×ρ×η1) wherein M fit is the annual loss of coal quantity in the coalfield fire area; a is the proportion of effective combustion area; A is the area of the fire area; H is the average coal seam thickness; p is the coal density; η1 is the combustion efficiency factor, which is 0.85±0.05 when the combustion type is open fire, 0.65±0.05 when the combustion type is smoldering, and is calculated by weighting according to the area proportion of open fire and smoldering when there are both open fire and smoldering.

3. The coalfield fire area atmospheric pollutant emission accounting method according to claim 2, characterized in that, The pollutants include nitrogen oxides, sulfur dioxide, particulate matter and volatile organic compounds; the emission factors of nitrogen oxides, sulfur dioxide, particulate matter and volatile organic compounds in the oxygen-rich state are 2.0 kg / t, 3.0 kg / t, 10 kg / t and 1.5 kg / t respectively; the emission factors of nitrogen oxides, sulfur dioxide, particulate matter and volatile organic compounds in the oxygen-poor state are 1.5 kg / t, 2.0 kg / t, 15 kg / t and 1.9 kg / t respectively.

4. The coalfield fire area atmospheric pollutant emission accounting method according to claim 3, characterized in that, The calculation method of the source strength is: Source strength = annual loss of coal quantity × pollutant emission factor.

5. The coalfield fire area atmospheric pollutant emission accounting method according to claim 1, characterized in that, The calculation expression of the migration and transformation coefficient is: η2 = η0 x K 深度 x K 裂隙 x K 覆盖层 Wherein, η2 is the migration and transformation coefficient; η0 is the basic migration coefficient, which is 1.0 by default; K 深度 is the fire source depth correction coefficient; K 裂隙 is the fissure development correction coefficient; K 覆盖层 is the overburden type and thickness correction coefficient; when the fire source depth is less than 50 meters, the fire source depth correction coefficient ranges from 0.9 to 1.0; when the fire source depth is greater than or equal to 50 meters and less than or equal to 100 meters, the fire source depth correction coefficient ranges from 0.7 to 0.8; when the fire source depth is greater than 100 meters, the fire source depth correction coefficient ranges from 0.5 to 0.6; when the fissure development degree is strong, medium, and weak, respectively, the fissure development correction coefficient corresponds to 1.0, 0.8-0.9, and 0.7-0.8, respectively; when the overburden is high, medium, and low permeability, respectively, the initial value of the overburden type and thickness correction coefficient corresponds to 1.0, 0.8-0.9, and 0.7, respectively, and when the thickness of the overburden is greater than or equal to 20 meters and increases by 10 meters, the overburden type and thickness correction coefficient is multiplied by 0.9 once.

6. The coalfield fire area atmospheric pollutant emission accounting method according to claim 5, characterized in that, When the fire source depth is less than 50 meters and the cover layer type is high-permeability type, medium-permeability type and low-permeability type respectively, the value of the migration coefficient synergistic factor is 1.0, 0.95 and 0.90 respectively; when the fire source depth is greater than or equal to 50 meters and less than or equal to 100 meters and the cover layer type is high-permeability type, medium-permeability type and low-permeability type respectively, the value of the migration coefficient synergistic factor is 1.05, 1.0 and 0.85 respectively; when the fire source depth is greater than 100 meters and the cover layer type is high-permeability type, medium-permeability type and low-permeability type respectively, the value of the migration coefficient synergistic factor is 1.10, 1.0 and 0.7 respectively.

7. The coalfield fire area atmospheric pollutant emission accounting method according to claim 1, characterized in that, When the pollutant release mode is point source release type, the value range of the release coefficient is 0.9-1; when the pollutant is area source release type, the value range of the release coefficient is 0.7-0.8; when the pollutant contains point source release type and area source release type at the same time, that is, excessive source release type, the value range of the release coefficient is 0.8-0.

9.

8. The coalfield fire area atmospheric pollutant emission accounting method according to claim 7, characterized in that, When the fracture development degree is weak development and the pollutant release mode is point source release type, excessive source release type and surface source release type, the value of the release coefficient synergy factor is 0.90, 0.85 and 0.75 respectively; when the fracture development degree is medium development and the pollutant release mode is point source release type, excessive source release type and surface source release type, the value of the release coefficient synergy factor is 1.0; when the fracture development degree is strong development and the pollutant release mode is point source release type, excessive source release type and surface source release type, the value of the release coefficient synergy factor is 1.05, 1.10 and 1.15 respectively.

9. The coalfield fire area atmospheric pollutant emission accounting method according to claim 1, characterized in that, The calculation expression of the atmospheric pollutant emission amount of the coalfield fire area is: Atmospheric pollutant emission amount of coalfield fire area = source strength × migration and transformation coefficient × release coefficient × migration coefficient synergy factor × release coefficient synergy factor.

10. A method for calculating the amount of reduction in pollution based on the method for calculating the amount of atmospheric pollutants emitted by a coalfield fire zone according to any one of claims 1 to 9, characterized in that, Including: The atmospheric pollutant emission amount of the coalfield fire area before and after treatment is obtained by using the atmospheric pollutant emission amount accounting method of the coalfield fire area, and then the treatment emission reduction amount is obtained; Wherein, the atmospheric pollutant emission amount of the coalfield fire area after treatment is collected and calculated on site after the completion of the treatment construction, or the basic information of the coalfield fire area, the coalfield geological channel information after the completion of the treatment construction are estimated by mathematical modeling method and calculated.

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