A method for calculating the explosion dangerous distance of hydrogen-doped natural gas pipeline leakage accident

Abstract

The application discloses a kind of hydrogen-doped natural gas pipeline leakage accident's explosion dangerous distance calculation method, belong to oil and gas safety technical field, comprising: step 1, according to the flow parameter of leakage hole under the condition of leakage;Step 2, establish hydrogen-doped natural gas pipeline leakage process mathematical model;Step 3, establish the geometric model of leakage area and divide grid;Step 4, determine the solution method of leakage model;Step 5, determine the explosion dangerous distance of hydrogen-doped natural gas pipeline leakage accident under different conditions;Step 6, fitting hydrogen-doped natural gas pipeline leakage accident's explosion dangerous distance calculation formula;Step 7, determine the accuracy of hydrogen-doped natural gas pipeline leakage accident's explosion dangerous distance calculation formula and application;The application is based on the fitting of hydrogen-doped natural gas pipeline leakage accident's explosion dangerous distance calculation formula according to the numerical simulation result of multiple conditions, can quickly calculate the explosion dangerous distance of leakage accident, provide guidance for the safety management of hydrogen-doped natural gas pipeline.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas safety, in particular to a calculation method of explosion dangerous distance of hydrogen-doped natural gas pipeline leakage accident. BACKGROUND

[0002] With the gradual depletion of fossil resources and the increasingly serious environmental problems, hydrogen energy is considered as one of the most potential energy alternatives in the future as a clean energy with abundant resources, high heat value and no carbon emissions. At present, hydrogen is mainly transported in the form of compressed hydrogen gas long tube trailer, liquid hydrogen and metal alloy hydrogen storage, but these methods have small storage and transportation scale, high cost and low efficiency. For long-distance transportation of hydrogen, pipeline is undoubtedly an economical and efficient choice. In order to shorten the transition period and consider economic and safety reasons, hydrogen is doped into natural gas at a certain proportion, and then transported by using existing natural gas pipeline or network, which is an effective way to realize large-scale transportation of hydrogen.

[0003] As known, both methane (CH4) and hydrogen (H2) are flammable and explosive gases, with explosion limit ranges of 5-15 vol% and 4-75.6 vol%, respectively. However, due to the wider explosion concentration limit range of hydrogen in air and the much lower minimum ignition energy than methane, CH4 / H2 mixture is more likely to be ignited and exploded once leaked, which seriously affects the safety of pipeline operation.

[0004] The explosion dangerous distance is crucial to evaluate the risk of hydrogen-doped natural gas pipeline leakage accident. The explosion dangerous distance of hydrogen-doped natural gas pipeline leakage accident can be determined by experiment or numerical simulation method. The experimental method is difficult to carry out due to safety factors. At present, the numerical simulation method is mainly used, but it is difficult to apply in engineering practice, and it is difficult to quickly calculate the explosion dangerous distance of hydrogen-doped natural gas pipeline leakage accident. SUMMARY

[0005] In view of the above problems, the present application fits a calculation formula of explosion dangerous distance of hydrogen-doped natural gas pipeline leakage accident based on the numerical simulation results of multiple working conditions, and proposes a calculation method of explosion dangerous distance of hydrogen-doped natural gas pipeline leakage accident, which can quickly calculate the explosion dangerous distance of leakage accident.

[0006] The present application is realized by the following technical solutions:

[0007] The above-mentioned calculation method of explosion dangerous distance of hydrogen-doped natural gas pipeline leakage accident comprises the following steps:

[0008] Step 1, selecting a typical hydrogen-doped natural gas pipeline leakage process as the research object, calculating the leakage hole flow parameters according to the leakage working condition, and taking it as the inlet boundary condition of the subsequent leakage model;

[0009] Leak hole pressure calculation formula:

[0010]

[0011] Wherein: p is the pipeline operating pressure, Pa; k is the adiabatic index; p e is the leak hole pressure, Pa;

[0012] Leak hole temperature calculation formula:

[0013]

[0014] Wherein: T is the pipeline operating temperature, K; T e is the leak hole temperature, K;

[0015] Leak rate calculation formula of small hole leakage:

[0016] When

[0017] When

[0018] Wherein: Q is the gas leakage rate, kg / s; C0 is the leak hole shape coefficient, wherein the circular is 1.00, the triangular is 0.95, and the rectangular is 0.90; d e is the leak hole diameter, m; M is the molar mass of the mixed gas, g / mol; R is the universal gas constant; p a is the environmental pressure, Pa; Z is the mixed gas compression factor;

[0019] Step 2, establish the mathematical model of hydrogen-doped natural gas pipeline leakage process, the basic control equation followed by the leakage process includes mass, momentum and energy conservation equation, also need to use the component transport equation to calculate the local mass fraction of each component in the leakage diffusion process, wherein the diffusion coefficient uses Fick diffusion coefficient matrix, the state equation uses Peng-Robinson equation, and the turbulence model selects k-ε model;

[0020] Component transport equation:

[0021]

[0022] Wherein: ρ is the density, kg / m 3 ; is the gas flow rate, m / s; t is the leakage time, s; Y i is the mass fraction of component i; is the diffusion flux of component i, kg / (m 2 ·s);

[0023] The multi-component diffusion coefficient needs to be calculated based on the binary diffusion coefficient, and the expression of the Fuller binary gas diffusion coefficient calculation model is as follows:

[0024]

[0025] In the formula: is the binary diffusion coefficient of component i in component j, m 2 / s; T is the temperature, K; p is the total pressure, Pa; M i and M j are the molar mass of components i and j, g / mol; V i and V j are the molecular diffusion volumes of components i and j, cm 3 ;

[0026] For an N-component system, the mass transfer process diffusion flux expression is as follows:

[0027]

[0028] In the formula: is the mass diffusion flux of component i, kg / (m 2 ·s); Y i is the mass fraction of component i; D ij is the generalized Fick diffusion coefficient, m 2 / s; The Fick diffusion coefficient matrix is composed of two parts, namely the Maxwell-Stefan diffusion coefficient matrix and the thermodynamic factor matrix:

[0029]

[0030] In the formula: is the Maxwell-Stefan diffusion coefficient matrix, which can be calculated by inverting the matrix [A]; [B] is the thermodynamic factor matrix; The expressions of matrix [A] and matrix [B] are as follows:

[0031]

[0032]

[0033]

[0034]

[0035] In the formula: X i and X j are the mole fractions of components i and j; M w is the molecular weight; m is the subscript used to define the average molecular weight in the mixture,

[0036] Step 3, a leakage area geometric model is established; a non-structural grid division method is used to divide the grid of the leakage area, the grid near the leakage hole is locally encrypted, and grid independence verification is carried out;

[0037] Step 4, determine the leakage model solving method; the leakage model inlet boundary condition is determined according to the leakage hole flow condition, and the outlet boundary adopts pressure outlet; a double-precision pressure solver is selected, and the SIMPLE algorithm is used for pressure-velocity coupling; in order to ensure the calculation accuracy, the turbulent kinetic energy and turbulent dissipation rate are discretized by using the second-order upwind scheme, and the transient equation is discretized by using the second-order implicit scheme;

[0038] Step 5, calculate the explosion lower limit of hydrogen-doped natural gas under different hydrogen-doped ratios; analyze the leakage and diffusion characteristics of hydrogen-doped natural gas under different working conditions, and determine the explosion danger distance of hydrogen-doped natural gas pipeline leakage accident under different pipeline operating pressures, leakage diameters and hydrogen-doped ratios;

[0039] The explosion lower limit calculation formula of hydrogen-doped natural gas is:

[0040]

[0041] In the formula, i and mix are gas components i and mixed gas respectively; Y i is the mole fraction of component i in the total combustible gas, %; LFL i is the explosion lower limit of component i, %; LFL mix is the explosion lower limit of the mixed gas, %; N is the number of combustible gas components;

[0042] Step 6, the explosion danger distance of hydrogen-doped natural gas pipeline leakage accident under different pipeline operating pressures, leakage diameters and hydrogen-doped ratios is multi-nonlinearly fitted, and the explosion danger distance calculation formula is determined:

[0043]

[0044] In the formula, EHD is the explosion danger distance of hydrogen-doped natural gas pipeline leakage accident, m; HBR is the hydrogen-doped ratio, %;

[0045] Step 7, the fitting formula calculation value of step 6 is compared with the numerical calculation result, the accuracy of the fitting formula is determined, and the fitting formula is used for rapid calculation of the explosion danger distance of hydrogen-doped natural gas pipeline leakage accident.

[0046] The above technical scheme is adopted in the application, and the following beneficial effects can be achieved:

[0047] The application provides a hydrogen-doped natural gas pipeline leakage explosion hazard distance calculation method, which guarantees the accuracy of explosion hazard distance calculation, greatly improves the calculation efficiency, and reduces the calculation cost to the maximum extent. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 The application provides a hydrogen-doped natural gas pipeline leakage explosion hazard distance calculation method, which guarantees the accuracy of explosion hazard distance calculation, greatly improves the calculation efficiency, and reduces the calculation cost to the maximum extent. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical scheme and advantages of the application clearer, the application is further described below in combination with the drawings in the embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and not used to limit the application.

[0050] As shown in the drawing, a hydrogen-doped natural gas pipeline leakage explosion hazard distance calculation method comprises the following steps: Figure 1 Step 1: a typical hydrogen-doped natural gas pipeline leakage process is selected as a research object, leakage hole flow parameters are calculated according to the leakage working condition, and the leakage hole flow parameters are used as inlet boundary conditions of a subsequent leakage model;

[0051] Step 2: a hydrogen-doped natural gas pipeline leakage process mathematical model is established, basic control equations followed by the leakage process include mass, momentum and energy conservation equations, and a component transport equation is used to calculate local mass fractions of each component in the leakage diffusion process, wherein a Fick diffusion coefficient matrix is used as a diffusion coefficient, a Peng-Robinson equation is used as a state equation, and a k-ε model is used as a turbulence model;

[0052] Step 3: a leakage area geometric model is established; a non-structural grid division method is used to divide the grid of the leakage area, the grid of the area near the leakage hole is locally encrypted, and grid independence verification is performed;

[0053] Step 4: a leakage model solving method is determined; the inlet boundary condition of the leakage model is determined according to the leakage hole flow condition, the outlet boundary is a pressure outlet, a double-precision pressure solver is selected, a SIMPLE algorithm is used for pressure-velocity coupling, in order to ensure the calculation accuracy, a second-order upwind format is used to disperse the turbulent kinetic energy and the turbulent dissipation rate, and a second-order implicit format is used for the transient equation;

[0054] Step 5: the lower explosion limit of hydrogen-doped natural gas under different hydrogen-doping ratios is calculated; the leakage diffusion characteristics of hydrogen-doped natural gas under different working conditions are analyzed, and the explosion hazard distance of the hydrogen-doped natural gas pipeline leakage accident under different pipeline operating pressures, leakage hole diameters and hydrogen-doping ratios is determined.

[0055]

[0056] ​Step 6, the explosion dangerous distance of the hydrogen-doped natural gas pipeline leakage accident under different pipeline operation pressures, leakage hole diameters and hydrogen-doping ratios is subjected to multi-element non-linear fitting to determine the explosion dangerous distance calculation formula;

[0057] Step 7, the fitting formula calculation value of step 6 is compared with the numerical calculation result to determine the accuracy of the fitting formula, and the fitting formula is used subsequently to quickly calculate the explosion dangerous distance of the hydrogen-doped natural gas pipeline leakage accident.

[0058] The application principle of the present application is further described below in combination with specific examples.

[0059] Step 1, a typical hydrogen-doped natural gas pipeline leakage process is selected as the research object, the leakage hole pressure, leakage hole temperature and leakage rate are calculated according to the leakage working conditions (pipeline operation pressure, leakage hole diameter and hydrogen-doping ratio), and the results are shown in Table 1, and are taken as the inlet boundary conditions of the subsequent leakage model;

[0060] Table 1 Flow parameters of the leakage hole under different leakage working conditions

[0061]

[0062] Step 2, a mathematical model of the hydrogen-doped natural gas pipeline leakage process is established, the basic control equations followed by the leakage process include mass, momentum and energy conservation equations, and a component transport equation is also needed to calculate the local mass fraction of each component in the leakage diffusion process, wherein the diffusion coefficient adopts a Fick diffusion coefficient matrix, the state equation adopts a Peng-Robinson equation, and the turbulence model selects a k-ε model;

[0063] Step 3, a leakage area geometric model is established; a non-structural grid division method is used to divide the grid of the leakage area, the grid near the leakage hole is locally encrypted, and grid independence verification is performed;

[0064] Step 4, the leakage model solving method is determined; the inlet boundary condition of the leakage model is determined according to the leakage hole flow condition, the outlet boundary adopts a pressure outlet; a double-precision pressure solver is selected, and a SIMPLE algorithm is used for pressure-velocity coupling; in order to ensure the calculation accuracy, the turbulent kinetic energy and turbulent dissipation rate are discretized by using a second-order upwind format, and the transient equation is discretized by using a second-order implicit format;

[0065] Step 5, the lower explosion limit calculation results of the hydrogen-doped natural gas under different hydrogen-doping ratios are shown in Table 2; the leakage diffusion characteristics of the hydrogen-doped natural gas under different working conditions are analyzed, and the explosion dangerous distance of the leakage accident is calculated, and the results are shown in Table 3;

[0066] Table 2 Lower explosion limit of hydrogen-doped natural gas

[0067]

[0068] Table 3 Explosion hazard distance of hydrogen-doped natural gas pipeline leakage accident

[0069]

[0070] Step 6: The explosion hazard distance of hydrogen-doped natural gas pipeline leakage accident under different pipeline operating pressures, leakage hole diameters and hydrogen-doping ratios was subjected to multiple nonlinear fitting to determine the explosion hazard distance calculation formula:

[0071]

[0072] In the formula, EHD is the explosion hazard distance of hydrogen-doped natural gas pipeline leakage accident, m; HBR is the hydrogen-doping ratio, %;

[0073] Step 7: The fitting formula calculation value of Step 6 was compared with the numerical calculation result, and the results are shown in Table 4. The deviation of the fitting formula is small, and the fitting formula is used for subsequent rapid calculation of the explosion hazard distance of hydrogen-doped natural gas pipeline leakage accident.

[0074] Table 4 Comparison of explosion hazard distance fitting formula calculation value and numerical calculation result

[0075]

Claims

1. A method for calculating the explosion danger distance of a hydrogen-doped natural gas pipeline leakage accident, characterized in that, The method comprises the following steps: Step 1, a typical hydrogen-doped natural gas pipeline leakage process is selected as the research object, the flow parameters of the leakage hole are calculated according to the leakage working condition, and the flow parameters are taken as the inlet boundary conditions of the subsequent leakage model; The pressure calculation formula of the leakage hole is: where: p is the pipe operating pressure, Pa; k is the adiabatic exponent; p e is the leak hole pressure, Pa; The temperature calculation formula of the leakage hole is: where: T is the pipe operating temperature, K; T e is the leak hole temperature, K; The leakage rate calculation formula of the small hole leakage is: When When where: Q is the gas leakage rate, kg / s; Co is the leakage hole shape coefficient, where a circle is 1.00, a triangle is 0.95, and a rectangle is 0.90; d e is the leakage hole diameter, m; M is the molar mass of the mixed gas, g / mol; R is the universal gas constant; p a is the ambient pressure, Pa; Z is the mixed gas compressibility factor; Step 2, a mathematical model of the hydrogen-doped natural gas pipeline leakage process is established, the basic control equations followed by the leakage process include mass, momentum and energy conservation equations, and a component transport equation is also used to calculate the local mass fraction of each component in the leakage diffusion process, wherein the diffusion coefficient adopts a Fick diffusion coefficient matrix, the state equation adopts a Peng-Robinson equation, and a k-ε model is selected as the turbulence model; The component transport equation is: where: p is the density, kg / m 3 ; is the gas flow rate, m / s; t is the leak time, s; Y i is the mass fraction of component i; is the diffusion flux of component i, kg / (m 2 ·s); The multi-component diffusion coefficient needs to be calculated based on the binary diffusion coefficient, and the expression of the Fuller binary gas diffusion coefficient calculation model is: wherein: Dijis the binary diffusion coefficient of component i in component j, m 2 T is the temperature, K; p is the total pressure, Pa; M i and M j are the molar masses of components i and j, respectively, g / mol; V i and V j are the molecular diffusion volumes of components i and j, respectively, cm 3 ; For an N-component system, the diffusion flux expression of the mass transfer process is: where: is the mass diffusion flux of component i, kg / (m 2 ·s); Y j is the mass fraction of component j; D ij is the generalized Fickian diffusion coefficient, m 2 / s; the Fickian diffusion coefficient matrix is composed of two parts, Maxwell-Stefan diffusion coefficient matrix and thermodynamic factor matrix: wherein: is the Maxwell-Stefan diffusion coefficient matrix, which can be calculated by matrix inversion of matrix [A]; [B] is the thermodynamic factor matrix; The expressions of matrix [A] and matrix [B] are: wherein: X i and X j are the mole fraction of components i and j, respectively; M w is the molecular weight; m is an index used to define the average molecular weight in the mixture, Step 3, a leakage area geometric model is established; a non-structural grid division method is used to divide the grid of the leakage area, the grid near the leakage hole is locally encrypted, and the grid independence is verified; Step 4, the leakage model solving method is determined; the inlet boundary condition of the leakage model is determined according to the flow condition of the leakage hole, the outlet boundary adopts a pressure outlet; a double-precision pressure solver is selected, and a SIMPLE algorithm is used for pressure-velocity coupling; in order to ensure the calculation accuracy, the turbulent kinetic energy and the turbulent dissipation rate are discretized by using a second-order upwind scheme, and the transient equation is discretized by using a second-order implicit scheme; Step 5, the lower explosion limit of hydrogen-doped natural gas under different hydrogen-doping ratios is calculated; the leakage and diffusion characteristics of hydrogen-doped natural gas under different working conditions are analyzed, and the explosion danger distance of the hydrogen-doped natural gas pipeline leakage accident under different pipeline operating pressures, leakage hole diameters and hydrogen-doping ratios is determined; The lower explosion limit calculation formula of hydrogen-doped natural gas is: where: i and mix are gas component i and mixture gas, respectively; Y i is the mole fraction of component i in the total combustible gas, %; LFL i is the lower flammable limit of component i, %; LFL mix is the lower flammable limit of the mixture gas, %; N is the number of combustible gas components; Step 6, the explosion danger distance of the hydrogen-doped natural gas pipeline leakage accident under different pipeline operating pressures, leakage hole diameters and hydrogen-doping ratios is multi-element nonlinearly fitted, and the explosion danger distance calculation formula is determined: In the formula, EHD is the explosion danger distance of the hydrogen-doped natural gas pipeline leakage accident, m; HBR is the hydrogen-doping ratio, %; Step 7, the fitting formula calculation value of step 6 is compared with the numerical calculation result, the accuracy of the fitting formula is determined, and the fitting formula is used for rapid calculation of the explosion danger distance of the hydrogen-doped natural gas pipeline leakage accident.

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