A Numerical Calculation and Hazard Assessment Method for the Leakage and Combustion Explosion of Hydrogen-Containing Natural Gas

Abstract

The present invention provides a numerical calculation and hazard assessment method for the leakage and combustion explosion of hydrogen-doped natural gas. The method includes: establishing a three-dimensional geometric model of the gate well space by using FLACS software; based on the hydrogen-doped natural gas leakage and diffusion model, calculating the change curve of the monitoring data of each monitoring point at different positions in the gate well space with time and the concentration distribution cloud map of hydrogen-doped natural gas by using FLACS software; performing numerical calculations of combustion and explosion based on the distribution cloud map to obtain the data of each monitoring point and the distribution cloud maps of jet flame, shock wave overpressure, and thermal radiation intensity; based on the numerical calculation results of combustion and explosion, calculating the probability of the thermal radiation and explosion shock wave generated by the explosion causing harm to the human body, so as to realize the assessment of combustion and explosion hazards. By adopting the probability function method to calculate the probability of different levels of damage to the human body when subjected to different shock wave overpressures and thermal radiations, the present invention can effectively evaluate the combustion and explosion hazards.

Description

Technical Field

[0001] The present invention belongs to the technical field of natural gas safety, and in particular relates to a numerical calculation and hazard assessment method for combustion and explosion caused by leakage of hydrogen-blended natural gas in a gate well space. Background Art

[0002] In response to global warming and accelerating green and low-carbon development, hydrogen energy, as a green, low-carbon and widely used secondary energy source, has become an important means to promote energy reform and achieve carbon neutrality. Hydrogen transportation is an important link in the hydrogen energy industry chain. Adding a certain proportion of hydrogen to natural gas to form hydrogen-blended natural gas, and then using the existing natural gas pipeline network for transportation, can greatly increase the scale and efficiency of hydrogen allocation. Compared with methane, hydrogen has a higher calorific value, diffusion rate, mass calorific value, and auto-ignition temperature. Therefore, the risk of combustion and explosion after leakage of hydrogen-blended natural gas has also increased. As the coverage area of ​​urban gas pipelines increases, the number of gas wells has gradually increased. Once a leak occurs in the gas well transmission and distribution pipeline, a flammable gas cloud will be formed inside the closed space of the well, which is very likely to cause fires, explosions and other safety accidents.

[0003] At present, the method of evaluating the hazard of combustible gas explosion can only roughly determine the degree of damage to the human body within different overpressure and thermal radiation ranges, but cannot determine the probability of causing different levels of damage to the human body. Large-scale hydrogen-blended natural gas leakage and explosion experiments have problems such as large required site, high cost, and high risk factor. With the continuous development of computational fluid dynamics, the use of numerical calculation methods for the study of combustible gas leakage and explosion is increasing. Many scholars at home and abroad have proved the feasibility of using FLACS software to simulate combustible gas leakage and explosion. FLACS software includes diffusion module, explosion module, hydrogen module, and fire module, which can accurately simulate the leakage and explosion of hydrogen-blended natural gas in the gate well space.

[0004] In view of this, the present invention proposes a numerical calculation and hazard assessment method for combustion and explosion caused by leakage of hydrogen-blended natural gas in a gate well space. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a numerical calculation and hazard assessment method for leakage and explosion of hydrogen-blended natural gas.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions.

[0007] A numerical calculation and hazard assessment method for leakage and explosion of hydrogen-blended natural gas, comprising the following steps:

[0008] Use FLACS software to establish a three-dimensional geometric model of the gate well space, complete mesh division, and set parameters based on local environmental parameters and real-time leakage conditions;

[0009] Based on the hydrogen - doped natural gas leakage diffusion model, use FLACS software to calculate the variation curves of the monitoring data at each monitoring point at different positions in the valve well space over time and the concentration distribution cloud map of hydrogen - doped natural gas;

[0010] Determine the type and parameters of the ignition source according to the actual working conditions, and perform numerical calculations of combustion and explosion based on the said distribution cloud map to obtain the data at each monitoring point and the distribution cloud maps of jet flame, shock wave overpressure, and thermal radiation intensity;

[0011] Based on the numerical calculation results of combustion and explosion, calculate the probability of the thermal radiation and explosion shock wave generated by the explosion causing harm to the human body, and realize the assessment of combustion and explosion hazards.

[0012] Furthermore, before establishing the three - dimensional geometric model of the valve well space, the method further includes: summarizing parameters based on gas leakage and combustion - explosion events in valve well spaces at home and abroad, and the parameters include: inner diameter of the pipeline leakage hole, pipeline transportation pressure, leakage point position, three - dimensional size parameters of the valve well space, and hydrogen - doped natural gas parameters.

[0013] Furthermore, the grids obtained by grid division satisfy: minimum unit volume > 0, size distortion rate < 0.85, and angle distortion rate < 0.85.

[0014] Furthermore, the environmental parameters include the temperature inside the valve well and the atmospheric space temperature, gravitational acceleration, atmospheric wind direction and wind speed; the real - time leakage conditions include leakage critical pressure, leakage point position, leakage aperture, leakage hole shape, leakage start time and duration.

[0015] Furthermore, the monitoring data of the monitoring points include hydrogen - doped natural gas concentration, shock wave velocity, explosion static pressure and dynamic pressure.

[0016] Furthermore, the types of ignition sources include:

[0017] Open flames: match flame, lighter flame, gas welding and gas cutting flame;

[0018] Hot objects: sparks, cigarette butts, welding slag;

[0019] Electric sparks: sparks generated by short - circuit, leakage, lightning strike, and static discharge sparks;

[0020] Sparks generated by impact and friction;

[0021] Objects ignited by focused light irradiation.

[0022] Furthermore, the ignition source parameters include: ignition source position, ignition source size, and ignition duration.

[0023] Furthermore, a leakage diffusion model of hydrogen - doped natural gas is established based on the light gas diffusion theory. The diffusion process includes an initial injection stage, a rising stage, and a turbulent diffusion stage. Among them, the initial injection stage is described by a small - hole leakage model, and the formula is as follows:

[0024] When the gas flow is subsonic, the gas leakage rate is:

[0025]

[0026] When the gas flow is sonic, the gas leakage rate is:

[0027]

[0028] In the formula, P a is the atmospheric pressure, P is the critical pressure at the leakage hole, k is the isentropic exponent of hydrogen - doped natural gas, which varies with the hydrogen - doping ratio; q m is the mass flow rate of the leakage hole, C g is the orifice flow coefficient, T is the gas temperature at the leakage point, M is the molar mass, and d or is the diameter of the leakage hole;

[0029] During the rising stage and the turbulent diffusion stage of hydrogen - doped natural gas, only component transport occurs between hydrogen - doped natural gas and air, and no heat exchange takes place. The component transport model is used to describe the concentration distribution during the diffusion of hydrogen - doped natural gas, and the formula is as follows:

[0030]

[0031] In the formula, ρ i is the density of component i, t is the diffusion time, u ij is the diffusion velocity of component i in the j - direction, C i is the volume concentration of component i, D air-i is the diffusion coefficient of component i in air, where i = 1, 2, 3, 4, 5, corresponding to components methane, hydrogen, ethane, propane, and carbon dioxide respectively; j = 1, 2, 3, representing the X, Y, and Z directions respectively.

[0032] Furthermore, the probability p of thermal radiation causing damage to the human body is:

[0033]

[0034] p r = c 1 + c 2 ln D(5)

[0035]

[0036] In the formula, F k is the influence coefficient of the harm to people when the clothes are not on fire, with a value range of 0.14 - 0.95, erf() is the error function, p r is the probability function, c 1 、c 2 are coefficients determined by the injury level. The injury levels include first-degree burns, second-degree burns, and death. D is the heat radiation dose value, and its calculation formula is:

[0037] D = t eff ×q 4 / 3 (7)

[0038] In the formula, t eff is the time when a person is exposed to the heat flux, q is the heat flux density calculated based on the fire type, and the calculation formula of q is:

[0039] q = SEP act ×F view ×τ a (8)

[0040] In the formula, SEP act is the actual surface emissive power, F view is the field of view coefficient, τ a is the atmospheric transmittance, and the calculation formula of τ a is:

[0041] τ a = c 3 [P w (X - R)] -0.09 (9)

[0042] In the formula, X is the distance from the target to the center of the flame, R is the radius of the center of the flame, and the constant c 3 = 2.02, P w is the partial pressure of water vapor in the air, and the calculation formula of P w is:

[0043]

[0044] In the formula, T is the air temperature, and RH is the relative humidity.

[0045] Furthermore, the probability p' of the shock wave causing damage to the human body is:

[0046]

[0047] p′ r = c′ 1 + c′ 2 ln S (12)

[0048] In the formula, p′r is a probability function, c′ 1 and c′ 2 are coefficients determined by the types of damage to the human body caused by an explosion, and the types of damage include lung injury, eardrum rupture, head injury, and human displacement injury; S is the value of the shock wave impact, and the calculation formulas for different types of damage are as follows:

[0049] Lung injury:

[0050] Eardrum rupture: S = P s ,

[0051] Skull injury:

[0052] Whole body displacement shock:

[0053] In the formula, is the scaled pressure, P s is the peak overpressure, P′ is the total overpressure at the location where the person is, P a is the ambient pressure, i is the scaled impulse, i s is the pulse value, t p is the duration of the positive phase of the overpressure, and m is the human body mass.

[0054] Compared with the prior art, the present invention has the following beneficial effects.

[0055] (1) The method of the present invention is applicable to the gas gate well spaces with different structures and sizes in the city, and can also be extended to limited enclosed spaces such as household kitchens and open spaces such as hydrogen refueling stations.

[0056] (2) The present invention adopts a multi-component gas leakage combustion explosion model, and considers the effects of different hydrogen blending ratios, different environmental conditions, real-time leakage conditions, etc. on leakage combustion explosion, and can better reveal the leakage diffusion law and combustion explosion damage effect of hydrogen-enriched natural gas.

[0057] (3) Compared with the traditional explosion hazard assessment method, the present invention uses the probability function method to calculate the probability of different levels of damage to the human body under different shock wave overpressures and thermal radiation states, which has great economic and social significance for personnel evacuation and property protection work after an accident. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 is a flowchart of a numerical calculation and hazard assessment method for hydrogen-enriched natural gas leakage combustion explosion according to an embodiment of the present invention.

[0059] Figure 2 is a three-dimensional structure diagram of two different forms of gate wells.

[0060] Figure 3 Schematic diagram of the change in the concentration of hydrogen-doped natural gas in the Y-Z plane when X = 1.2 m after a pipeline leak in the gate well.

[0061] Figure 4 Schematic diagram of the distribution of the combustible gas cloud after a pipeline leak in the gate well.

[0062] Figure 5 Static overpressure change diagram after the combustion and explosion of hydrogen-doped natural gas in the gate well space.

[0063] Figure 6 Dynamic overpressure change diagram after the combustion and explosion of hydrogen-doped natural gas in the gate well space.

[0064] Figure 7 Thermal radiation temperature change diagram after the combustion and explosion of hydrogen-doped natural gas in the gate well space. Specific implementation manners

[0065] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described below in conjunction with the accompanying drawings and specific implementation manners. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0066] Figure 1 The flowchart of a numerical calculation and hazard assessment method for the leakage, combustion and explosion of hydrogen-doped natural gas according to an embodiment of the present invention includes the following steps:

[0067] Step 101: Use FLACS software to establish a three-dimensional geometric model of the gate well space, complete the mesh division, and set parameters in combination with local environmental parameters and real-time leakage conditions;

[0068] Step 102: Based on the hydrogen-doped natural gas leakage and diffusion model, use FLACS software to calculate the change curve of the monitoring data of each monitoring point at different positions in the gate well space over time and the concentration distribution cloud map of hydrogen-doped natural gas;

[0069] Step 103: Determine the type and parameters of the ignition source according to the actual working conditions, and perform numerical calculations of combustion and explosion based on the distribution cloud map to obtain the data of each monitoring point and the distribution cloud maps of the jet flame, shock wave overpressure, and thermal radiation intensity;

[0070] Step 104: Based on the numerical calculation results of combustion and explosion, calculate the probability of the thermal radiation and explosion shock wave generated by the explosion causing harm to the human body, and realize the combustion and explosion hazard assessment.

[0071] In this embodiment, step 101 is mainly used to establish a three-dimensional geometric model of the gate well space. In this embodiment, the FLACS software is used to establish the model. FLACS is a CFD software for simulating gas leakage and explosion behaviors and is now widely used in the oil and gas industries. The FLACS software includes a CASD pre-processing unit, a Simulations solution calculation unit, and a Flowvis post-processing unit, which are used to establish a three-dimensional geometric model, perform simulation calculations, and output calculation data, respectively. FLACS has been verified by a large amount of experimental data, and the simulation results are highly accurate, accurate, and reliable. In addition to modeling, this embodiment also needs to complete mesh generation and set leakage parameters in combination with local environmental parameters and real-time working conditions. In this embodiment, referring to the national building standard design reference atlas 05s502, the CASD pre-processing software in FLACS is used to establish a three-dimensional geometric model of the gate well space from three parts: Materials, Objects, and Geometry, as Figure 2 shown. Taking the single manhole cover gate well model as an example, its dimensions are 2.4m×3.4m×2.85m, the wall thickness is 0.3m, the manhole cover diameter is 0.8m, and the thickness is 0.02m. In the DIRECTION in the main menu GRID, select the X, Y, and Z directions respectively. The calculation area is set to 2.4m×3.4m×6m. Uniform grids are used in the horizontal direction along the leakage hole, and variable grids are used in the direction perpendicular to the leakage hole. The "smooth" command is used to make the two different width-sized grids have a smooth transition. The percentage difference coefficients in the X, Y, and Z directions are 10.31, 9.95, and 19.03 respectively, all less than 20, and the total number of grids is 329232.

[0072] In this embodiment, step 102 is mainly used to calculate the monitoring data of each monitoring point at different positions in the gate well space. In this embodiment, by establishing a hydrogen-doped natural gas leakage diffusion model, multiple data monitoring points are set at different positions in the gate well space, and the FLACS software is used to calculate the change values of the monitoring data of each monitoring point over time. Based on the calculation results of each monitoring point, a distribution cloud map of hydrogen-doped natural gas leakage in the gate well space at a certain plane position and a certain moment is calculated, as Figure 3 、 4 shown. It can be seen from Figure 3 that the hydrogen-doped natural gas jets upward from the leakage hole in the form of a jet under the action of the pipeline pressure, hits the top and then disperses around, and then diffuses towards the edge and bottom due to the pressure difference and concentration difference between the hydrogen-doped natural gas and the surrounding environment, causing the concentration inside the gate well space to gradually rise. When t = 1000s, the overall concentration of the cross-section is close to 13%. It can be seen from Figure 4 that the volume of the combustible gas cloud increases rapidly in the interval of 370s to 400s, from less than 1m3 to filling the entire gate well space, reaching 11.467m3.

[0073] In this embodiment, step 103 is mainly used for numerical calculation of combustion explosion. In this embodiment, the type and parameters of the ignition source are first determined according to the actual working conditions, and then numerical calculation of combustion explosion is carried out based on the distribution cloud map obtained in step 102 to obtain the data of each monitoring point and the distribution cloud maps of jet flame, shock wave overpressure, and thermal radiation intensity, as shown respectively in Figures 5 - 7 as shown. The static pressure cloud map of the shock wave is as shown in Figure 5 as shown. At t = 200 ms, the shock wave pressure reaches the maximum bearing pressure of the manhole cover, and the manhole cover is damaged and starts to relieve pressure outward. At t = 245 ms, a negative pressure appears above the manhole cover, and the influence range is a sphere centered on the manhole cover. At t = 290 ms, the internal pressure of the gate well reaches the maximum overpressure, and then the pressure shows a gradually decreasing trend. The dynamic pressure cloud map of the shock wave is as shown in Figure 6 as shown. In the initial stage of the explosion, the dynamic pressure appears at the position of the manhole cover opening, and the maximum value can reach 14000 Pa. Then the shock wave moves upward, and the highest influence range reaches 5 m above the manhole cover. The thermal radiation temperature cloud map is as shown in Figure 7 as shown. The hydrogen-doped natural gas in the gate well explodes when encountering an open fire. In the initial stage of the explosion, the flame spreads out spherically around the ignition source, and the central temperature can reach 2200 K. Then the shock wave breaks through the manhole cover, and the flame also spreads out from the manhole cover opening, reaching up to 10 m above the manhole cover at most.

[0074] In this embodiment, step 104 is mainly used for evaluating the combustion explosion hazard. Based on the numerical calculation results of the combustion explosion, this embodiment calculates the probabilities of the thermal radiation and explosion shock wave generated by the explosion causing harm to the human body respectively to achieve the evaluation of the combustion explosion hazard. The greater the probability, the greater the combustion explosion hazard. The following embodiments will respectively give the calculation methods of the two harm probabilities.

[0075] As an alternative embodiment, before establishing the three-dimensional geometric model of the gate well space, the method further includes: summarizing parameters based on the gas leakage and combustion explosion events in the gate well space at home and abroad, and the parameters include: inner diameter of the pipeline leakage hole, pipeline transportation pressure, leakage point position, three-dimensional size parameters of the gate well space, and hydrogen-doped natural gas parameters.

[0076] This embodiment gives a technical solution for data collection before modeling. Before modeling, it is necessary to sort out and summarize the gas leakage and combustion explosion events in the gate well space at home and abroad to obtain the basic parameters required for simulating the leakage and combustion explosion of hydrogen-doped natural gas in the gate well space, including hydrogen-doped natural gas pipeline parameters (inner diameter of the leakage hole, pipeline transportation pressure, leakage point position, etc.), three-dimensional size parameters of the gate well space, and hydrogen-doped natural gas parameters (hydrogen doping ratio, properties of methane and hydrogen, etc.).

[0077] As an alternative embodiment, the grids obtained by grid division satisfy: minimum unit volume > 0, size distortion rate < 0.85, and angle distortion rate < 0.85.

[0078] This embodiment provides quality inspection criteria for mesh generation, including the minimum element volume, size distortion rate, and angular distortion rate. If the minimum element volume is greater than 0 and both the size distortion rate and the angular distortion rate are less than 0.85, the mesh inspection is qualified. The mesh distortion rate refers to the difference between this mesh and a standard cube mesh with the same volume. The size distortion rate is calculated based on the mesh element size, and the angular distortion rate is calculated based on the element included angle, ranging from 0 to 1, and the smaller the value, the better the quality.

[0079] As an alternative embodiment, the environmental parameters include the temperature inside the sluice well and the atmospheric temperature, gravitational acceleration, atmospheric wind direction and wind speed; the real-time leakage conditions include the leakage critical pressure, leakage point location, leakage aperture, leakage hole shape, leakage start time and duration.

[0080] This embodiment provides several specific environmental parameters and real-time leakage condition parameters. The environmental parameters include the temperature inside the sluice well and the atmospheric temperature, gravitational acceleration, atmospheric wind direction and wind speed. For example, the temperature inside the sluice well and the atmospheric temperature are set to 20 °C, the gravitational acceleration is set to 9.8 m / s 2 , it is set to "NOZZLE" when there is no wind on the ground and "WIND" when there is wind. The wind speed is given by the value of WIND_SPEED, the local atmospheric pressure is set to the standard atmospheric pressure of 101 KPa, the ground roughness is set to 0.01 m, the relative turbulence intensity is set to 0.1, and the atmospheric stability is set to F. The real-time leakage conditions include the leakage critical pressure, leakage point location, leakage aperture, leakage hole area, leakage start time and duration. For example, the pipeline operating pressure is 0.4 MPa, the leakage point is located in the middle of the flange connection, and the area is 1.5 mm 2 .

[0081] As an alternative embodiment, the monitoring data of the monitoring point includes the concentration of hydrogen-enriched natural gas, shock wave velocity, explosion static pressure, and dynamic pressure.

[0082] This embodiment provides the monitoring data of the monitoring point. The monitoring data of this embodiment is mainly the concentration of hydrogen-enriched natural gas, shock wave velocity, explosion static pressure, and dynamic pressure.

[0083] As an alternative embodiment, the types of ignition sources include:

[0084] Open flames: match flame, lighter flame, gas welding and gas cutting flame;

[0085] Hot objects: sparks, cigarette butts, welding slag;

[0086] Electric sparks: sparks generated by short circuits, leakage, lightning strikes, and static discharge sparks;

[0087] Sparks generated by impact and friction;

[0088] An object ignited by focused light irradiation.

[0089] This embodiment gives several common types of ignition sources. In order to improve the accuracy of numerical calculations of combustion and explosion, different ignition sources are distinguished in the numerical calculations of combustion and explosion in this embodiment. The main types of ignition sources in this embodiment are mainly the following five categories: open flames, hot objects, electric sparks, sparks generated by impact and friction, and objects ignited by focused light irradiation. Some categories can be further subdivided. For example, open flames include match flames, lighter flames, gas welding and gas cutting flames, etc.; hot objects include sparks, cigarette butts, and welding slag, etc.

[0090] As an optional embodiment, the ignition source parameters include: ignition source position, ignition source size, and ignition duration.

[0091] This embodiment gives several ignition source parameters. The ignition source parameters in this embodiment mainly include the ignition source position, the ignition source size, and the ignition duration.

[0092] As an optional embodiment, a hydrogen-doped natural gas leakage diffusion model is established based on the light gas diffusion theory. The diffusion process includes an initial injection stage, a rising stage, and a turbulent diffusion stage; among them, the initial injection stage is described by a small-hole leakage model, and the formula is as follows:

[0093] When the gas flow is subsonic, the gas leakage amount is:

[0094]

[0095] When the gas flow is sonic, the gas leakage amount is:

[0096]

[0097] In the formula, P a is the atmospheric pressure, P is the critical pressure at the leakage hole, k is the isentropic index of hydrogen-doped natural gas, which changes with the hydrogen doping ratio; q m is the mass flow rate of the leakage hole, C g is the orifice flow coefficient, T is the gas temperature at the leakage point, M is the molar mass, d or is the diameter of the leakage hole;

[0098] During the rising stage and the turbulent diffusion stage of hydrogen-doped natural gas, only component transport occurs between hydrogen-doped natural gas and air, and no heat exchange occurs. The component transport model is used to describe the concentration distribution during the diffusion of hydrogen-doped natural gas, and the formula is as follows:

[0099]

[0100] Where ρ i is the density of component i, t is the diffusion time, u ij is the diffusion velocity of component i in the j direction, C i is the volume concentration of component i, D air-i is the diffusion coefficient of component i in air, where i = 1, 2, 3, 4, 5, corresponding to components methane, hydrogen, ethane, propane, and carbon dioxide respectively; j = 1, 2, 3, representing the X, Y, and Z directions respectively.

[0101] This embodiment presents a leakage diffusion model for hydrogen - blended natural gas. The leakage diffusion process of hydrogen - blended natural gas follows the three major laws of mass conservation, momentum conservation, and energy conservation. Based on these three laws, a leakage diffusion model for hydrogen - blended natural gas can be derived. Since the density of hydrogen - blended natural gas is lower than that of air, its leakage diffusion process can be described by the light - gas diffusion theory. In this embodiment, the leakage diffusion process is divided into an initial jet stage, a rising stage, and a turbulent diffusion stage, and diffusion models for different stages are given respectively. The initial jet stage is described by the small - hole leakage model, and the diffusion models are as shown in equations (1) and (2); in the rising stage and the turbulent diffusion stage, only component transport (transfer and exchange between different components) occurs between hydrogen - blended natural gas and air, and no heat exchange occurs. The component transport model is used to describe the concentration distribution during the diffusion of hydrogen - blended natural gas, as shown in equation (3).

[0102] As an alternative embodiment, the probability p of heat radiation causing damage to the human body is:

[0103]

[0104] p r = c 1 + c 2 ln D (5)

[0105]

[0106] Where F k is the influence coefficient of unburned clothing on human injury, with a value range of 0.14 - 0.95, erf() is the error function, p r is the probability function, c 1 , c 2 are coefficients determined by the injury level. The injury levels include first - degree burns, second - degree burns, and death. D is the heat radiation dose value, and its calculation formula is:

[0107] D = t eff × q 4 / 3 (7)

[0108] Where t eff is the time a person is exposed to the heat flux, q is the heat flux density calculated based on the fire type, and the calculation formula for q is:

[0109] q = SEP act × F view × τ a (8)

[0110] Wherein, SEP act is the actual surface emission power, F view is the field of view coefficient, τ a is the atmospheric transmittance, τ a The calculation formula of is:

[0111] τ a = c 3 [P w (X - R)] -0.09 (9)

[0112] Wherein, X is the distance from the target to the center of the flame, R is the radius of the center of the flame, and the constant c 3 = 2.02, P w is the partial pressure of water vapor in the air, P w The calculation formula of is:

[0113]

[0114] Wherein, T is the air temperature and RH is the relative humidity.

[0115] This embodiment gives the calculation formula of the probability of thermal radiation causing damage to the human body. The probability of thermal radiation causing damage to the human body is one of the indexes for evaluating explosion injury, and its calculation formula is as shown in formulas (4) to (10). Here, each formula will not be elaborated in detail, and only the probability function p r in the formula of is solved for the values of c 1 , c 2 for introduction. c 1 , c 2 are determined by the injury level, and the injury levels include first-degree burns, second-degree burns and death. Table 1 gives a set of values corresponding to each level.

[0116] Table 1 Coefficient c 1 , c 2 Values

[0117] Injury level <![CDATA[c 1 > <![CDATA[c 2 > First-degree burn -39.83 3.0186 Second-degree burn -43.14 3.0186 Death -36.38 2.56

[0118] As an alternative embodiment, the probability p' of the shock wave causing damage to the human body is:

[0119]

[0120] p′ r = c′ 1 + c′2 ln S (12)

[0121] In the formula, p′ r is the probability function, and c 1 ′, c′ 2 are coefficients determined by the types of damage to the human body caused by the explosion. The types of damage include lung injury, eardrum rupture, head injury, and human displacement injury; S is the shock wave impact value. The calculation formulas for different types of damage are as follows:

[0122] Lung injury:

[0123] Eardrum rupture: S = P s ,

[0124] Skull injury:

[0125] Whole body displacement shock:

[0126] In the formula, is the scaled pressure, P s is the peak overpressure, P′ is the total overpressure at the location where the person is, P a is the ambient pressure, i is the scaled impulse, i s is the pulse value, t p is the positive phase duration of the overpressure, and m is the human body mass.

[0127] This embodiment gives the calculation formula for the probability of damage to the human body caused by the shock wave. The probability of damage to the human body caused by the shock wave is also one of the indicators for evaluating the explosion injury. Its calculation formulas are as shown in formulas (11) and (12). S is the shock wave impact value, and the coefficients c′ 1 , c′ 2 and S all vary with the different types of damage to the human body caused by the explosion. The types of damage include lung injury, eardrum rupture, head injury, and human displacement injury. The calculation formulas for S corresponding to different types of damage are as above; the values of c′ 1 , c′ 2 are shown in Table 2.

[0128] Table 2 Values of coefficients c′ 1 , c′ 2

[0129] Injury type <![CDATA[c′ 1 > <![CDATA[c′ 2 > Lung injury 5.0 -5.74 Tympanic membrane rupture -12.6 1.524 Head injury 5.0 -8.49 Human displacement injury 5.0 -2.44

[0130] ​As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A numerical calculation and hazard assessment method for leakage and explosion of hydrogen-blended natural gas, characterized in that: The following steps are involved: Use FLACS software to establish a three-dimensional geometric model of the gate well space, complete meshing, and set parameters based on local environmental parameters and real-time leakage conditions; Based on the leakage and diffusion model of hydrogen-blended natural gas, the FLACS software is used to calculate the change curve of monitoring data at each monitoring point at different positions in the gate well space over time and the distribution cloud map of hydrogen-blended natural gas concentration; Determine the type and parameters of the ignition source according to the actual working conditions, and perform numerical calculations of the combustion and explosion based on the distribution cloud map to obtain data of each monitoring point and a distribution cloud map of the jet flame, shock wave overpressure, and thermal radiation intensity; Based on the numerical calculation results of combustion and explosion, the probability of thermal radiation and explosion shock waves generated by the explosion causing harm to the human body is calculated to achieve combustion and explosion hazard assessment; The probability p' of a shock wave causing damage to the human body is: p′ r =c′1+c′2lnS (12) In the formula, p r ′ is a probability function, c1′ and c′2 are coefficients determined by the types of damage to the human body caused by the explosion, including lung damage, eardrum rupture, head damage and human displacement damage; S is the impact value of the shock wave, and the calculation formula for different damage types is as follows: Lung damage: Ruptured eardrum: S = P s , Skull injuries: Whole body displacement impact: In the formula, is the scale pressure, P s is the peak overpressure, P′ is the total overpressure at the location where the person is located, and P a is the ambient pressure, i is the scale impulse, i s is the pulse value, t p is the duration of the positive phase of overpressure, and m is the mass of the human body.

2. The method for numerical calculation and hazard assessment of leakage and explosion of hydrogen-blended natural gas according to claim 1 is characterized in that: Before establishing the three-dimensional geometric model of the gate well space, the method also includes: summarizing parameters based on the gas leakage and explosion incidents in the gate well space occurring at home and abroad, wherein the parameters include: the inner diameter of the pipeline leakage hole, the pipeline pressure, the location of the leakage point, the three-dimensional size parameters of the gate well space, and the parameters of the hydrogen-blended natural gas.

3. The method for numerical calculation and hazard assessment of leakage and explosion of hydrogen-blended natural gas according to claim 1, characterized in that: The mesh obtained by mesh division satisfies: minimum unit volume>0, size distortion rate<0.85, and angle distortion rate<0.

85.

4. The method for numerical calculation and hazard assessment of leakage and explosion of hydrogen-blended natural gas according to claim 1, characterized in that: The environmental parameters include the internal temperature of the gate shaft and the atmospheric space temperature, gravitational acceleration, atmospheric wind direction and wind speed; the real-time leakage conditions include the critical leakage pressure, leakage point location, leakage aperture, leakage hole shape, leakage start time and duration.

5. The method for numerical calculation and hazard assessment of leakage and explosion of hydrogen-blended natural gas according to claim 1, characterized in that: The monitoring data of the monitoring points include the concentration of hydrogen-blended natural gas, shock wave velocity, explosion static pressure and dynamic pressure.

6. The method for numerical calculation and hazard assessment of leakage and explosion of hydrogen-blended natural gas according to claim 1, characterized in that: The ignition source types include: Open flame: match flame, lighter flame, gas welding and gas cutting flame; High temperature objects: sparks, cigarette butts, welding slag; Electric sparks: sparks caused by short circuit, leakage, lightning strike, and static discharge sparks; Sparks from impact and friction; Focus the light on the object that is burning.

7. The method for numerical calculation and hazard assessment of leakage and explosion of hydrogen-blended natural gas according to claim 1, characterized in that: The ignition source parameters include: ignition source position, ignition source size, and ignition duration.

8. The method for numerical calculation and hazard assessment of leakage and explosion of hydrogen-blended natural gas according to claim 1, characterized in that: Based on the light gas diffusion theory, a leakage diffusion model of hydrogen-blended natural gas is established. The diffusion process includes the initial injection stage, the rising stage and the turbulent diffusion stage. Among them, the initial injection stage is described by the small hole leakage model, and the formula is as follows: when When , the gas flow is subsonic flow, and the gas leakage is: when When , the gas flow is sonic flow, and the gas leakage is: Where P a is the atmospheric pressure, P is the critical pressure at the leak hole, k is the isentropic index of hydrogen-doped natural gas, which changes with the change of hydrogen-doped ratio; q m is the mass flow rate of the leak hole, C g is the orifice flow coefficient, T is the gas temperature at the leakage point, M is the molar mass, d or is the leakage hole diameter; During the rising stage and turbulent diffusion stage of hydrogen-blended natural gas, only components are transported between the natural gas and the air, but no heat is exchanged. The component transport model is used to describe the concentration distribution of hydrogen-blended natural gas during diffusion. The formula is as follows: In the formula, ρ i is the density of component i, t is the diffusion time, u ij is the diffusion velocity of component i in direction j, C i is the volume concentration of component i, D air-i is the diffusion coefficient of component i in the air, where i=1,2,3,4,5, corresponding to components methane, hydrogen, ethane, propane and carbon dioxide respectively; j=1,2,3, representing the X, Y and Z directions respectively.

9. The method for numerical calculation and hazard assessment of leakage and explosion of hydrogen-blended natural gas according to claim 8, characterized in that: The probability p of thermal radiation causing damage to the human body is: p r =c1+c2lnD (5) In the formula, F k is the influence coefficient of the clothes on the injury to the person when they are not on fire, and the value is 0.14~0.95, erf() is the error function, p r is a probability function, c1 and c2 are coefficients determined by the injury level, which includes first-degree burns, second-degree burns and death, and D is the thermal radiation dose value. The calculation formula is: D=t eff ×q 4 / 3 (7) Where, t eff is the time people are exposed to the heat flux, q is the heat flux density calculated based on the fire type, and the calculation formula of q is: q=SEP act ×F view ×τ a (8) In the formula, SEP act is the actual surface emission power, F view is the field of view coefficient, τ a is the atmospheric transmittance, τ a The calculation formula is: τ a =c3[P w (XR)] -0.09 (9) Where X is the distance from the target to the flame center, R is the radius of the flame center, constant c3 = 2.02, P w is the partial pressure of water vapor in the air, P w The calculation formula is: Where T is the air temperature and RH is the relative humidity.

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